(CNN) - The United Nations team investigating a chemical weapons attack last month in Syria has found that sarin was used.
"In particular, the environmental, chemical and medical samples we have collected provide clear and convincing evidence that surface-to-surface rockets containing the nerve agent sarin were used in Ein Tarma, Moadamiyah and Amalaka in the Ghouta area of Damascus," a 38-page report says.
Chemical weapons "were used on a relatively large scale," U.N. Secretary-General Ban Ki-moon said in a briefing to the U.N. Security Council.
It's "the most significant confirmed use of chemical weapons against civilians since Saddam Hussein used them in Halabja in 1988," Ban said.
The U.N. mission "adhered to the most stringent protocols available for such an investigation, including to ensure the chain of custody for all samples," Ban added.
The team interviewed survivors and first responders, and collected hair, urine and blood samples.
"The Mission also documented and sampled impact sites and munitions, and collected 30 soil and environmental samples -- far more than any previous such United Nations investigation," Ban said.
The report presents a stark picture of the horrific events of August 21.
"Survivors reported that following an attack with shelling, they quickly experienced a range of symptoms, including shortness of breath, disorientation, eye irritation, blurred vision, nausea, vomiting and general weakness," Ban said. "Many eventually lost consciousness. First responders described seeing a large number of individuals lying on the ground, many of them dead or unconscious."
The weather made things worse. Falling temperatures at the time of the attack meant the downward movement of air, allowing the gas "to easily penetrate the basements and lower levels of buildings and other structures where many people were seeking shelter," Ban said.
The U.N. mission has not completed its investigation of other alleged uses of chemical weapons in Syria, Ban said.
But there's no doubt chemical weapons were used in the attack last month, he said.
"The United Nations Mission has now confirmed, unequivocally and objectively, that chemical weapons have been used in Syria."
"This is a war crime and a grave violation of the 1925 Protocol and other rules of customary international law. I trust all can join me in condemning this despicable crime. The international community has a responsibility to hold the perpetrators accountable and to ensure that chemical weapons never re-emerge as an instrument of warfare."
The U.N. mission's mandate, however, did not include assigning blame for the attack.
It was not immediately clear whether the report will affect events on the ground in Syria, where more than 100,000 people have been killed in 2½ years of conflict, the vast majority by conventional weapons, according to U.N. estimates.
Turkish fighter jets downed a Syrian helicopter near the border between the two countries Monday, Turkey's semiofficial Anatolia News Agency reported, citing Deputy Prime Minister Bulent Arinc.
It's unclear how the U.N. report may affect international dynamics of the Syrian conflict.
The United States, Britain, France, and NATO have said that Syrian President Bashar al-Assad's regime was behind the attack and that there's no sign rebels had access to such weapons.
Human Rights Watch said al-Assad's forces "were almost certainly responsible,"
But Syria and its ally Russia have blamed rebels.
The United States and Russia reached an agreement over the weekend aimed at averting U.S. military action against the Syrian regime. President Obama, on Monday, called that "an important step."
"We're not there yet. But if properly implemented, this agreement could end the threat these weapons pose not only to the Syrian people, but to the world," he said.
Russia slams U.S. remarks on agreement
Even as the world awaited the report Monday, Russia openly bickered with the United States about the agreement.
The deal calls for a U.N. resolution demanding that Syria's chemical weapons be placed under international control.
Russian Foreign Minister Sergey Lavrov accused U.S. Secretary of State John Kerry "and his Western allies" Monday of misunderstanding the deal, according to Russia's state-run Itar-Tass news agency.
The deal does not say the U.N. resolution will be under Chapter 7 of the U.N. Charter, Lavrov said.
Chapter 7 potentially authorizes the use of force.
Lavrov said comments by Kerry "show unwillingness to read the document" that Russia and the United States agreed to.
Kerry said Monday that a U.N. resolution will need to include the possibility of force. "If the Assad regime believes that this is not enforceable, then they will play games," he said.
"Should diplomacy fail, the military option is still on the table," he told reporters.
The agreement states that if there is noncompliance "or any use of chemical weapons by anyone in Syria, the U.N. Security Council should impose measures under Chapter VII of the U.N. Charter."
It does not specifically state that the resolution being sought now will be under that chapter.
Russia, a Syrian ally, holds veto power on the council.
"A week ago, the Syrian regime did not admit that it even had chemical weapons," Kerry told reporters Monday. "Today, that regime has agreed, at least through the Russians ... to rid itself of those weapons."
But he also noted that "nothing can be accepted at face value."
According to the plan, Syria must submit a full list of its chemical weapons stockpile within a week. International inspectors must be on the ground in the country by November, and all production equipment must be destroyed by the end of November.
By the middle of next year, all chemical weapons material must be destroyed, according to the agreement.
A daunting task
The process of securing and destroying Syria's cache of chemical weapons -- in the middle of a civil war -- will be a logistical nightmare.
U.S. intelligence suggests that Syria has about 1,000 metric tons of chemical weapons, most of it sarin and VX stored as unmixed components, Kerry said last week. Sarin and VX are nerve gases that can cause convulsions, paralysis, respiratory failure and death.
To complicate matters, U.S. officials and Syrian rebels suspect the regime has been moving some if its chemical weapons.
So the Syrian regime is basically on the honor system.
Then there's the matter of where the weapons will be taken, and how.
The U.S. and Russia say they're working on the details. They say they'll submit something in the next few days.
The destruction process will be carried out by personnel from both the United Nations and the Organisation for the Prohibition of Chemical Weapons, which implements the international ban on chemical weapons use, according to the Kerry-Lavrov plan.
Opposition group wants more
Even if Syria's chemical weapons disappear, that won't stop the daily bloodshed on the ground.
The opposition Syrian National Coalition wants a ban on the regime's use of air power and ballistic weapons against population centers.
"We understand that removing the chemical weapons still leaves him with artillery and airplanes, and he uses them indiscriminately against his people," Kerry said. "And we are going to do everything in our power to continue to push towards the political resolution that is so critical to ending that violence."