(CNN) -- The United States expanded its Iraq air campaign over the weekend to beat back Islamist militants determined to kill members of a religious minority.
Fighter jets and drones struck ISIS fighters firing on ethnic Yazidis near the northern town of Sinjar, where extremists had driven tens of thousands fleeing into nearby mountains.
Iraqi officials said U.S. airstrikes Saturday killed 16 fighters from the Islamic State of Iraq and Syria, the extremist militia that calls itself the Islamic State.
An Iraqi airstrike in Sinjar killed an additional 45 ISIS fighters and injured 60 on Friday, Iraq state media reported.
Airdrops not enough
On Saturday, three U.S. cargo planes, accompanied by U.S. fighter jets, airdropped 3,804 gallons of fresh drinking water and 16,128 ready-to-eat meals to Yazidis stranded in the mountains, the military said.
But the airstrikes and humanitarian airdrops aren't enough to help the estimated 40,000 Yazidis, a United Nations official said.
The group comprises ethnic Kurds who practice a religion that draws from Zoroastrianism, Christianity and Judaism. ISIS considers all who do not practice their strict interpretation of Sunni Islam heretics and executes them.
It has placed the heads of it victims on spikes in cities it has captured and posted videos of savage executions online.
60 children dead
Iraqi security forces have only been able to airlift about 100 to 150 people a day off of Sinjar Mountain, said Marizio Babille of UNICEF, the UN's children agency. And time is running out for many who cannot reach the airdropped supplies.
Dozens, including 60 children, have died on the mountain, where the Yazidis are battling extreme temperatures, hunger and thirst.
Britain and France have said they will join the United States in the airdrops. And on Sunday, a British C130 cargo plane delivered aid supplies to Iraq, a Ministry of Defense spokesman said.
But UNICEF wants to see international actors help open a humanitarian corridor over land -- a safe escape route -- to evacuate the besieged people.
Protecting U.S. interests
Last week, President Barack Obama authorized targeted attacks not only to protect Iraqi minorities from ISIS' murderous rampage, but also Americans stationed in the Kurdish regional capital of Irbil.
Hundreds of U.S. military personnel are in Iraq, including advisers sent in recently to coordinate local military officials fighting ISIS. Many of them and U.S. consular staff are based in Irbil.
Obama cautioned that the campaign will be a "long-term project." "I don't think we're going to solve this problem in weeks," the President told reporters Saturday.
But he reiterated his vow that no U.S. combat troops will join the fight.
Striking ISIS also defends the United States' interests at home, the President said Saturday. Terrorists massing in Syria and Iraq could lash out at Western targets, he said.
"There's going to be a counterterrorism element that we are already preparing for and have been working diligently on for a long time now," Obama said.
ISIS' blitz advances have surprised policy makers and analysts in and outside of Iraq, the President said.
But also he said the lack of a cohesive Iraqi government makes them possible. It is dominated by Shiite Muslim factions and has been accused of mistreating Iraqi Sunnis.
The administration is putting pressure on Baghdad to reform, including replacing Prime Minister Nuri al-Maliki.
Many young Sunni men have joined ISIS, which has set up recruitment offices in their region. And Iraqi government forces have been known to dissolve and flee in the face of ISIS advances.
Even with the strikes, there was news that ISIS militants have captured Iraq's largest hydroelectric dam, just north of Mosul, Iraq's second-largest city.
The militant fighters have been using U.S.-made weapons seized during fighting from the Iraqi army, including M1 Abrams tanks, local officials said.
There had been conflicting reports about who controlled the dam on the Tigris River, with heavy fighting under way between ISIS fighters and Kurdish forces, known as Peshmerga.
U.S. officials have warned that a failure of the dam would be catastrophic, resulting in flooding all the way to Baghdad.