House Speaker Nancy Pelosi warned the Trump administration against taking military action in Iran without authorization from Congress, as the U.S. weighs how to respond to rising tensions in the Middle East.

"The responsibility in the Constitution is for Congress to declare war," Pelosi said Thursday. "So I hope that the president's advisers recognize that they have no authorization to go forward in any way."

Pelosi said that the 2001 Authorization for the Use of Military Force — or AUMF — enacted by Congress after the Sept. 11 terrorist attacks would not cover actions taken against Iran. She said that, like President Donald Trump, she opposed the 2003 invasion of Iraq, and she welcomed reports this week that the president had "no appetite" for war, a characterization offered by Republican Sen. Mitt Romney.