The Pentagon declined to discuss whether the U.S. military would step in with airstrikes to help Iraqi forces struggling to recapture Tikrit one day after a successful mission in assisting Iraq forces reclaim a strategic dam from Islamic militants.

“I’m not going to speculate about future operations,” Rear Adm. John Kirby, the Pentagon spokesman, told reporters Tuesday.

President Obama and U.S. military leaders have authorized airstrikes in Iraq only under two main missions: to provide humanitarian assistance and to protect U.S. personnel and facilities.

Kirby said U.S. airstrikes were “critical” in dislodging Islamic State fighters from the Mosul dam, which Iraqi and Kurdish forces retook Monday. He said that airstrike operation fell under the mission of protecting U.S. personnel and facilities 90 miles away in Irbil because any damage to the dam could flood the surrounding area.

Iraqi army units supported by Shiite militias early Tuesday launched an operation aimed at retaking Tikrit, the birthplace of former dictator Saddam Hussein, from the Islamic State. But Iraqi soldiers reportedly were stopped in their tracks south and west of the city when they came under heavy fire.

When it comes to airstrikes, Kirby said for now the U.S. is sticking to its two main missions while helping provide strategic advice to the Iraqi army.

“We can assist where we can, but this is theirs to fight,” he said.