(CNN) - The specter of chemical weapons attacks in the Syrian civil war emerged Tuesday, with the government and rebels each blaming the other for using such munitions.
The embattled government of President Bashar al-Assad accused rebels of a deadly chemical weapons missile attack. At least 25 people died and dozens more were injured Tuesday in the town of Khan al-Asal in Aleppo province, Syrian state media said, quoting government figures. Rebels rebuffed the claims and blamed the regime.
The town of Ateibeh, in eastern Damascus, endured "fierce shelling with chemical rockets," an opposition group said. An unknown number of casualties were reported.
These claims come amid pressure in the West to arm rebels, long overmatched by the Syrian military and its allies. The United States and other world powers have worried that Syria would consider using its chemical weaponry arsenal against fighters trying to topple the al-Assad government. And there is concern that jihadists who are fighting on the side of the opposition could get their hands on chemical weaponry.
The civil war -- which had its beginning two years ago after a government crackdown on Syrian protesters -- has left around 70,000 people dead, the United Nations said, and uprooted more than 1 million people.
Syrian Information Minister Omran al-Zoubi said the missile in Aleppo province was launched from inside Syria, but the launcher came from another country.
"Whoever paid for this weapon in Qatar or any other country and whoever brought this weapon to be used in Syria must be held accountable, whoever they are, a king or a prince, a president or a minister," he said. "Whoever made this decision in the last Arab League meeting is responsible for the mass killing and the use of weapons of destruction."
Jamal al Ward, head of the military office of the Syrian Coalition, said the opposition has "no chemical substances and no mechanism for producing" such weapons.
"The regime has these weapons and everyone knows where they keep them. They have missiles and factories where they make missiles with chemicals. They are the ones capable of using this stuff all over Syria," he said. "I know the (rebel) battalions and the weapons they have in that area and they just don't have chemicals."
The state-run Syrian Arab News Agency, which reported that most of those killed were civilians, showed photos on its website of people being treated in hospitals.
But Louay Almokdad, political and media coordinator for the Free Syrian Army, told CNN that the rebels lack access to chemical weapons and surface-to-surface missiles. He confirmed injuries in an attack in the town, but said it was carried out with a missile possessed only by the regime.
"The area that was targeted is under rebels' control, so it is quite absurd that the regime would accuse us of attacking our own people," he said.
"The Assad regime possesses chemical agents and they already used weapons of mass destruction against its own people, so we do expect the worse from this brutal psychopathic regime," he said. "The international community must take these attacks against our civilian population seriously. It is time to put an end to the daily mass killings in Syria."
An activist Facebook page said the location was between rebel-held and regime-held territory, and it appeared that the blast hit mostly regime soldiers, and some civilians in a regime-held area.
As for Ateibeh, the shelling caused deaths and many injuries, "including suffocating and nausea cases and headache, vomiting and hysteria cases," the opposition Local Coordination Committees of Syria said.
"These cases are being documented for the first time in the town and were not seen like this before," the LCC said. There was no immediate government comment about Ateibeh.
Homemade videos show injured people and others say witnesses talked of people suffocating.
International reaction: Shock, concern, skepticism
The international community is looking into the reports. The Russian Foreign Ministry, citing information from Damascus, said chemical weapons were used by the armed opposition, causing deaths and injuries.
"We believe the new incident is an extremely alarming and dangerous development in the Syrian crisis," the Russian ministry said. "Russia is seriously concerned about the fact of (weapons of mass destruction) coming into the hands of militants, which makes the situation in Syria even worse and brings the confrontation in the country to a new level."
The Obama administration is carefully investigating the reports, White House spokesman Jay Carney said.
"Any time we see reports of chemical weapons use in Syria it's a top priority to try to determine what happened," he said. Carney reiterated President Barack Obama's position that the use of chemical weapons by al-Assad or those under his command would be "totally unacceptable."
"There will be consequences and they will be held accountable," Carney said, passing along the president's comment
Carney also said there's no evidence to support the claim that the opposition has used chemical weapons. Obama will be discussing the Syrian crisis during his visit this week to the Middle East, where it will be a topic of conservation with Israeli, Jordanian and Palestinian leaders.
The British Foreign Office is also checking on the reports.
"The use of chemical weapons would be abhorrent and universally condemned. The UK is clear that the use or proliferation of chemical weapons would demand a serious response from the international community and force us to revisit our approach so far," a spokesman said.
Two senior U.S. officials said they don't believe the rebels used chemical weapons and suggested the regime itself may have manufactured the incident to preserve the ability use them in the future.
"The regime is using (the claims) as a pretext for their own possible use," one of the officials said. "The opposition has no such weapons."
The officials said they could not confirm a rebel claim that the regime used some type of agent on its own people in order to blame the rebels, but could not rule it out. Officials pointed to previous claims that chemical weapons were used, which after extensive investigation were unsubstantiated.
The Syrian government did not use chemical weapons against residents of Homs in a December attack, a U.S. State Department investigation showed, but did apparently misuse a riot-control gas in the incident, according to senior U.S. officials.
The investigation stemmed from allegations inside Syria about the use of chemical weapons during the attack on the city of Homs on December 23. The officials said the State Department launched a probe from its consulate in Istanbul after doctors and activists reported dozens of victims suffering from nervous system, respiratory and gastrointestinal ailments after inhaling the gas.
Military analysts believe the Syrian government may have one of the largest stockpiles of chemical weapons in the world. Specifically, the supply could include sarin, mustard and VX gases.
Arming the rebels
Dissidents inside and outside Syria have called for the United States to take a greater role in helping Syrian rebels, including supplying arms.
So far, the Obama administration has donated nonlethal and humanitarian aid.
But Secretary of State John Kerry said the United States would not stand in the way of its allies' arming Syrian rebels.
Kerry acknowledged the need to change the military "imbalance" on the ground in order to change al-Assad's "calculus."
"Right now, President Assad is receiving help from the Iranians, he's receiving help from al Qaeda-related, some elements, he's receiving help from Hezbollah, and obviously some help is coming in through the Russians," Kerry said. "If he believes he can shoot it out, Syrians and the region have a problem and the world has a problem."
Members of the rebel Free Syrian Army have said they've received shipments from some countries and seized and purchased weapons from government troops. But al-Assad's forces have heavy weaponry and warplanes.
Last week, the French foreign minister said he wanted to lift a European Union arms embargo and start arming rebels.
"We must go ahead and allow the Syrian people to defend themselves against this bloodthirsty regime. It's our responsibility to help the (opposition) Syrian National Coalition, its leaders and the Free Syrian Army by all the possible means," Laurent Fabius wrote in an op-ed for the French newspaper Liberation.
"If not, the slaughter will continue, and there will not be any other possible outcome but to strengthen the most extreme groups and the collapse of Syria with devastating consequences for the country itself and the region."
In February, the European Union renewed its arms embargo on Syria for three months -- but amended it to allow greater nonlethal support and technical assistance to help protect civilians.
The latest EU arms embargo is set to expire in May. Member countries could renew it, add amendments or veto it.
A new opposition leader
A Syrian opposition alliance elected Ghassan Hitto, an information technology executive and U.S.-educated Kurdish businessman, to lead its provisional government.
The National Coalition for Syrian Revolutionary and Opposition Forces made the announcement Tuesday.
The contingent government's formation should assuage concerns from the West -- particularly the United States -- about who would lead Syria should al-Assad be deposed, the Syrian American Council said.
"This question has now been answered," the group said.
For two years, the lack of a clear alternative to al-Assad's government has hampered the opposition's efforts in gaining more international support. Some say the absence of an alternative leader has helped prolong the bloodshed.
It didn't take long for Hitto to declare what many in the opposition have said: "There will be no dialogue with the Assad regime."
The opposition's new prime minister has both Syrian and American roots.
Born in Damascus, Hitto earned his bachelor's and master's degrees from Indiana universities and lived for many years in Dallas, where he worked as an information technology executive.
But he remained active in Syrian causes, serving on the board of the Syrian American Council and visiting the besieged country several times, the National Coalition said.
He left his job of 11 years to work full-time for the Syrian revolution and directed the alliance's assistance coordination unit.
Hitto and his wife, an American teacher, have four children. Their oldest son has helped with humanitarian aid in Syria and was injured in a bombing, the group said.