The White House invited Pelosi and other senior lawmakers from both parties to join President Trump in the White House Situation Room Thursday afternoon for a classified briefing.
After hearing the administration lay out its intelligence, Pelosi said Trump did not share any options for a response he is considering, adding she could not predict what actions the president might take next.
"How we go forward from here has to be strategic and smart and in close alliance with our, our allies that we have a common interest in the region," she said. "We know that the high tension wires are up there and we must do everything we can not to escalate the situation, but also to make sure that our personnel and the region are safe."
Senate Minority Leader Chuck Schumer told reporters that he made clear to Trump that any military action the administration is mulling must be approved first by Congress.
"The President may not intend to go to war here, but we're worried that he and the administration may bumble into a war," Schumer, D-N.Y., said, speaking to reporters back on Capitol Hill. "We told the room that the Democratic position is that Congressional approval must be required before funding any conflict in Iran."
Pelosi also emphasized that any "military activities" taken by the United States would require a new authorization of military force.
"On every occasion that we are engaged with the administration, in terms of our national security, we make it very clear that in order to get engaged in any military activities we must have a new authorization of use of military force," she said.
Pelosi said she does not know the array of military options the Department of Defense has presented to the president.
"He knows, but he did not share that with us," she said. "I cannot really predict what actions the White House will take. They did consult with us. We had an opportunity to share our thoughts with the administration. The president said we’ll have more meetings like this. I don't know what the sequence of that will be."
Returning from the White House, Senate Majority Leader Mitch McConnell told reporters that the administration told lawmakers that the U.S. drone was fired on from Iranian soil and struck in international waters.
"We had a good briefing," McConnell, R-Kentucky, said. "I think the administration is engaged in measured responses."
Earlier Thursday, the top congressional leaders from both parties and chairmen and ranking members of the Intelligence, Foreign Affairs and Armed Services Committees – totaling more than 20 lawmakers – were invited to a closed-door, classified intelligence briefing from the administration at the Capitol late Thursday morning.
"I think it's a dangerous situation," Pelosi, D-California, said during a news conference at the Capitol Thursday morning. "We have to be strong and strategic about how we protect our interests. We also cannot be reckless in what we do. So it would be interesting to see what they have to say, whether the - I don't think the president wants to go to war. There's no appetite for going to war in our country."
The White House invited top members of Congress to the White House Situation Room Thursday to learn more about the administration’s position on Iran from Chairman of the Joint Chiefs of Staff Gen. Joseph Dunford, outgoing acting Secretary of Defense Patrick Shanahan and his replacement Mark Esper. The top four congressional leaders – Pelosi, House Minority Leader Kevin McCarthy, Senate Majority Leader Mitch McConnell and Senate Minority Leader Chuck Schumer, as well as the chairmen and ranking members of the House and Senate Armed Services and Intelligence committees are all expected to attend.
"There's nobody who has any illusions about Iran, their bad behavior in terms of who they support in the region, their spreading of ballistic missiles – and we have sanctions on all of that," Pelosi said prior to the briefing. "But this is a dangerous neighborhood and miscalculation on either side could provoke something that would be very bad in terms of the security and our interests."
Sen. Lindsey Graham, R-South Carolina, told reporters that Trump's response to Iranian provocation "is truly a defining moment for him," likening it to the moment when President Barack Obama drew a "red line" and vowed he would not let Syrian President Bashar al-Assad get away with using chemical weapons on Syrians in 2013. Graham predicted the president's response will impact how adversaries around the world view the United States.
"If they do anything else to an American asset and this president doesn’t respond like Ronald Reagan, then this is a signal to Iran," Graham said, hours after conferring with the president on the phone Thursday morning. "We’re a lot closer today than we were yesterday and only God knows what tomorrow brings."
"They are testing him. They need to do so at their own peril," he added. "If they get away with this, God help us with North Korea and throughout the world. I'm convinced that as a last resort, President Trump will stop this behavior."
Earlier Thursday, Pelosi made clear she is not yet supporting a U.S. military response, but added, "let's get the facts."
"Let's make sure that we don't have a beating the drum for something without the clarity of the facts involved," she warned. "Our responsibility is to protect and defend our constitution, the American people, our country. That's our first responsibility. That's what we will honor."
Senate Majority Whip John Cornyn, the No. 2 ranked Republican in the upper chamber, warned that rhetoric encouraging military force was "reckless."
"I don't think Iran or the US wants a war," Cornyn, R-Texas, said. "The United States needs to respond appropriately and I'm sure the president's national security team is presenting him with a range of responses. If we do nothing, it just encourages Iran further and Iran has a long history of harassing and killing American. I think doing nothing would be a mistake."
Asked why tensions are rising between Iran and the United States, Pelosi pointed at the breakup of the Iran nuclear deal.
"When we moved away from that, we lost some credibility with our allies," she said. "However we go forward, we have to recognize that working together with our allies is very, very important and that we cannot throw our weight around."
ABC News' Trish Turner contributed to this report