The United States has launched two additional air strikes on Islamist militants in Iraq, who are targeting Kurdish forces defending the northern city of Irbil.

Islamic State fighters, who have beheaded and crucified captives in their drive to eradicate unbelievers, have advanced to within a half hour’s drive of Arbil, capital of Iraq’s Kurdish region and a hub for U.S. oil companies.

They have also seized control of Iraq’s biggest dam, Kurdish authorities confirmed on Friday, which could allow them to flood cities and cut off vital water and electricity supplies.

The Pentagon said two F/A-18 aircraft from an aircraft carrier in the Gulf had dropped laser-guided 500-pound bombs on the fighters’ artillery and other air strikes had targeted mortar positions and an Islamic State convoy

American planes conducted a second airdrop of food and water early Saturday for those trapped in the Sinjar mountains, said Pentagon chief spokesman Rear Adm. John Kirby. Escorted by two Navy fighter jets, three planes dropped 72 bundles of supplies for the refugees, including more than 28,000 meals and more than 1,500 gallons of water, said Kirby, who spoke from New Delhi during a trip with U.S. Defense Secretary Chuck Hagel.

“ISIS will not make a costly, futile stand to resist US air superiority, and their substantial territorial gains in recent months offer plenty of room to retreat. Unless the group is targeted in northern and eastern Syria, it will adapt and continue to threaten Iraq’s central government, Kurdish forces and rival Syrian rebels,” counterterrorism expert elaborated.

“These airstrikes were most likely precipitated by the Islamic States’ recent military gains in northern Iraq. There is now a threat to the critical Kurdish city of Irbil. Reports that ISIS now controls the Mosul dam — Iraq’s largest, and a critical strategic asset — have raised US concerns over the group’s gains and entrenchment,” stressed Itani, an analyst at the Atlantic Council.

The Pentagon also launched drone and manned aircraft attacks on artillery, a mortar position and a convoy that the Islamic State was using against Kurdish forces defending the northern city of Irbil on Friday.