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President Barack Obama authorized "targeted airstrikes" to protect U.S. interests in Iraq and airdrops of meals and water to refugees trapped on a mountaintop in northwest Iraq.

In a nationally televised address, Obama said Thursday night that he had long warned the Islamic State of Iraq and al-Sham, or ISIS, not to threaten the strategic city of Erbil. With ISIS fighters nearing it on Thursday, Obama said he had approved "targeted strikes against [ISIS] convoys should they approach the city."

"Today, America is coming to help," Obama said — while also stressing that U.S. troops wouldn't be returning to Iraq. The president added that he had also authorized targeted airstrikes to help break ISIS' siege trapping about 40,000 Christians and members of a religious sect called the Yazidi on Mount Sinjar near Mosul. "These innocent families are faced with a choice — descend and be slaughtered or stay and slowly die of hunger," he said. "We can act responsibly to prevent an act of genocide."

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After attempts by the Iraqi military to airdrop supplies to the refugees failed to provide relief, a senior U.S. defense official told NBC News on Thursday that "a number of U.S. military aircraft" had already successfully delivered food and water and had "safely exited the immediate airspace" without a shot having been fired.

The mission was conducted from multiple airbases supporting one C-17 and two C-130 transport aircraft, a defense official said. They were escorted by two F/A-18 Hornet combat jets.

The planes dropped 56 bundles of fresh drinking water and 16 bundles carrying 8,000 meals-ready-to-eat. They were over the drop area for less than 15 minutes, the official told NBC News.

Iraq's ambassador to the U.N., Mohamed Alhakim, earlier told reporters that his government had very limited resources to help the tens of thousands besieged. "It's unfortunate, and this is why this is a catastrophe," he said.

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The Associated Press contributed to this report.