ALQOSH, Iraq — Seizing on the momentum of focused American airstrikes in recent days, Kurdish forces moved to retake the strategic Mosul Dam on Sunday night, in their most significant challenge yet to the Sunni militants’ advance in northern Iraq.

The American assaults hit 10 armed vehicles, seven Humvees, two armored personnel carriers and one checkpoint belonging to fighters of the Islamic State in Iraq and Syria, the United States Central Command said Sunday.

In the past two days, United States forces have conducted 30 airstrikes across Iraq, officials said, with many of them focused around the dam, which militants captured after routing the Kurdish forces 10 days ago. A statement from the National Security Council in Washington on Sunday said that the bombings were ordered by President Obama to help the Iraqi forces “retake and establish control over the Mosul Dam.”

Mr. Obama, the statement added, also officially informed Congress that he had authorized the American airstrikes in Iraq, consistent with the War Powers Resolution.