WASHINGTON (AP) — The Latest on the United States and Iran (all times local):

3:30 p.m.

Top administration officials and lawmakers are arriving at the White House for a briefing about Iran's downing of an American surveillance drone in the Middle East amid mounting tension between the U.S. and Iran.

The White House invited House and Senate leaders of both parties and Democrats and Republicans on the House and Senate intelligence and Armed Services committees to meet with President Donald Trump on Thursday.

It's unclear if Trump is planning a U.S. response. He told reporters that Iran made a "very big mistake" but also said he has the feeling that it might have been the result of someone being "loose" or doing something "stupid."

Acting Defense Secretary Patrick Shanahan and Army Secretary Mark Esper, who Trump has said he'll nominate as defense secretary, also arrived for the meeting.

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3:10 p.m.

Democratic presidential candidate Joe Biden says that President Donald Trump has made military conflict with Iran more likely and that "another war in the Middle East is the last thing we need."

Biden made the remarks Thursday as tensions between Washington and Tehran escalated over the downing of an American drone over Iranian airspace.

Biden says Trump's strategy in Iran is "a self-inflicted disaster" since Trump withdrew the U.S. from the Iran nuclear agreement negotiated when Biden was vice president.

Biden says there's no question that Iran "continues to be a bad actor that abuses human rights and supports terrorist activities." But he says the U.S. needs presidential leadership at this moment.

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2:55 p.m.

Democratic presidential candidate Kirsten Gillibrand is demanding that President Donald Trump abstain from sending American troops into a conflict with Iran without congressional approval.

The New York senator outlined her position in a sharply worded letter to the White House on Thursday.

Gillibrand writes that she's "deeply concerned that your administration's stepped up military presence in the Middle East, in conjunction with your dangerous and confusing rhetoric, may lead the United States into a protracted, costly, and unnecessary war with Iran. Such a war is not authorized, would unnecessarily risk the lives of Americans and our allies, cause enormous human suffering, and destabilize the economy."

Gillibrand's position is not unique in her party, but she becomes one of the first Democratic presidential candidates to share her concerns with the White House directly.

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1:50 p.m.

The White House is inviting House and Senate leaders for a briefing with President Donald Trump on Thursday afternoon to discuss tensions with Iran.

That's according to two people familiar with the invitation who requested anonymity because they were not authorized to discuss it.

In addition to House and Senate leaders of both parties, the White House extended the invitation to the top Democrats and Republicans on the House and Senate intelligence and Armed Services committees.

The briefing comes after Iran's Revolutionary Guard shot down a U.S. surveillance drone. Trump said it might have been a mistake executed by someone just being "loose and stupid" and was coy about whether the U.S. would respond. He told reporters, "you'll find out."

— Mary Clare Jalonick

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12:35 p.m.

President Donald Trump is playing down Iran's downing of an American drone, saying that it might have been a mistake executed by someone just being "loose and stupid."

Trump told reporters Thursday that the shoot down of the drone was a "new wrinkle" in escalating tensions between the U.S. and Iran — a "fly in the ointment."

He was coy about whether the U.S. would respond, saying only that "you'll find out."

He said he has a feeling that it was a mistake — that a "general or somebody" made a mistake in shooting that drone down.

But he added that Iran made a "big mistake" and that the U.S. "will not stand for it."

Trump's words appear to signal that there may not be an immediate U.S. response to the incident.

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12:20 p.m.

President Donald Trump says Iran made a "very big mistake" when it shot down a U.S. drone, but he isn't saying how the U.S. plans to respond, saying only "you're going to find out."

Trump is speaking to reporters while meeting with Canadian Prime Minister Justin Trudeau as tensions between Washington and Tehran escalated over the downing of the drone, the U.S. exit from the 2015 Iran nuclear deal and sanctions crippling Iran's economy.

Iran's Revolutionary Guard said it shot down the drone over Iranian airspace. The U.S. military is calling the downing an "unprovoked attack" and said it occurred over international airspace in the Strait of Hormuz.

Trump said: "It was in international waters."

Iran's Revolutionary Guard says it shot down the RQ-4 Global Hawk drone over Iranian airspace.

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12:20 p.m.

A senior U.S. military official says Iran shot down an unmanned American aircraft over international waters in an attempt to disrupt U.S. efforts to monitor the Persian Gulf area.

Air Force Lt. Gen. Joseph Guastella says the shooting down of the drone follows recent threats to international shipping commerce in the region that the U.S. has blamed on Iran.

The commander of U.S. Central Command air forces in the region disputed Iranian claims that the drone was over Iranian air space.

Guastella told reporters Thursday that the aircraft was at high altitude and at least 34 kilometers from Iranian territory when it was shot over the Gulf of Oman.

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11:05 a.m.

House Speaker Nancy Pelosi says the U.S. cannot be "reckless" amid rising tensions with Iran.

Pelosi said Thursday she doesn't think President Donald Trump wants to go to war. And she said the American people don't want war either.

"There's no appetite for going to war in our country," she said.

The country needs to be "strong and strategic" about protecting its interests, Pelosi said, and "cannot be reckless."

Pelosi called a caucus-wide meeting of Democrats for later Thursday on Iran. House and Senate leadership will also be briefed by administration officials.

Tensions between Tehran and Washington have been rising over the collapsing nuclear deal with world powers. On Thursday, Iran's Revolutionary Guard shot down a U.S. surveillance drone.

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10:20 a.m.

President Donald Trump declared Thursday that "Iran made a very big mistake" in shooting down a U.S. drone.

White House press secretary Sarah Sanders says Trump was briefed Wednesday night and again Thursday morning about the incident. She says the administration also will keep in touch with lawmakers on Capitol Hill.

Trump made his comment on Twitter in midmorning.

American and Iranian officials are disputing the circumstances of the incident.

Iran's Revolutionary Guard said it shot down the drone over Iranian airspace. The U.S. military is calling the downing an "unprovoked attack" and said it occurred over international airspace in the Strait of Hormuz.