Washington — President Barack Obama says the recapturing of Mosul dam in northern Iraq by Iraqi and Kurdish forces is a "major step forward" in the battle against Islamic State militants.

Speaking at the White House, Obama said Monday that if the dam on the Tigris River had been breached it could have had catastrophic consequences and endangered American Embassy personnel in Baghdad.

Obama said the U.S. is urgently providing arms and assistance to Iraqi security forces as well as Kurdish fighters as they seek to reverse the Islamic State fighters' recent gains.

A new round of U.S. airstrikes in northern Iraq on Monday was aimed at helping Iraqi forces regain control of the Mosul dam and averting a potential dam failure, the Pentagon said.

U.S. Central Command said U.S. fighters, bombers and drone aircraft conducted 15 strikes around the dam, hitting Islamic State fighting positions as well as an anti-aircraft artillery gun and other weaponry of the Islamic State group that has captured wide swaths northern and western Iraq this summer.

The White House notified Congress by letter on Sunday that U.S. warplanes were engaged in strikes aimed at helping Iraq regain control of the dam.

The letter said "failure of the Mosul dam could threaten the lives of large numbers of civilians, threaten U.S. personnel and facilities — including the U.S. Embassy in Baghdad — and prevent the Iraqi government from providing crucial services to the Iraqi populace."

A Pentagon spokesman, Army Col. Steve Warren, said Monday the U.S. had no indication of the dam's imminent failure but is determined to prevent that possibility, which would pose a humanitarian disaster for populations along the Tigris river.

Warren said the U.S. airstrikes are part of a broader mission aimed at protecting U.S. personnel and facilities and preventing humanitarian disasters.

"Our mission is to strike ISIL targets to set the conditions for (Iraqi government) forces to take control of the dam," Warren said, using the acronym for the Islamic State in Iraq and the Levant, or simply the Islamic State.

"What we want to do is prevent (Islamic State) reinforcements" and reduce their defenses in order to help Iraqi forces to maneuver around the dam, he added.

The 15 U.S. airstrikes on Monday were in addition to 16 on Sunday and nine on Saturday. The Pentagon refused to identify the specific types of aircraft used in the airstrikes around the Mosul dam, citing restrictions imposed by the countries in the Middle East that are allowing the U.S. to use their air bases.