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

Pelosi specifically argued the current authorization for use of military force (AUMF), which was passed to fight terrorists in Afghanistan following the 9/11 attacks, would not extend to a confrontation with Iran.

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"They cannot call the authorization, AUMF, the authorization for the use of military force that was passed in 2001, as any authorization to go forward in the Middle East now," she said.

The existing AUMF has been used by presidents of both parties to launch operations well beyond its initial target of Afghanistan. And many lawmakers on both sides of the aisle say it needs updating to fit the current conflict, which has extended into Syria, terrorist hotspots in Africa and beyond. (A separate AUMF, passed in 2003 to authorize the invasion of Iraq, has since expired.)

“I think any action this administration takes will be thoughtful … and will be in consultation with the House and the Senate,” McCarthy, a close Trump ally, told reporters. He added the Trump administration is simply shifting U.S. resources in order to deter a military conflict with Iran.

“There is no action that’s being taken. You’re putting a hypothetical out there."

Asked at the White House Thursday if the U.S. intends to go to war with Iran, Trump responded in three words: "I hope not," he said

Pelosi said she's heartened by the noninterventionist position Trump has supported in the past, including his criticisms of the Iraq War, which Pelosi opposed. She's hoping he extends that approach to Iran.

"I like what I hear from the president, that he has no appetite for this," she said. "One of the places that I agree with the president is ... in our opposition to the war in Iraq. And I hope that that same attitude will prevail with the president of the United States, even though some of his supporters are rattling sabers."

Lawmakers in both chambers — including a growing number of Republicans — are voicing concerns that the administration has left Congress in the dark about the motivations for the escalation with Iran.

Pelosi amplified that criticism on Thursday, hammering administration officials for what she considers their failure to brief congressional lawmakers on hot spots around the world, including Venezuela and North Korea.

"This is part of a pattern that's not right because we have responsibilities," she said.

She went on lump Iran in that group, lamenting that only a small select group of lawmakers — the Gang of Eight, of which Pelosi is a part — are scheduled to be briefed on the reasons behind the buildup in confronting Iran.

"We're hoping that, for sure before the break, we'll have a classified briefing on the Middle East, on Iran, for the full House of Representatives. We will have one for the Gang of Eight later this afternoon, but that is no substitute for the full membership of the Congress, having that access," Pelosi said.

"There may be particular things that only we can hear, but that's not to undermine the responsibility that the administration has to making sure that the full Congress has the information."

Scott Wong contributed.