President Donald Trump told reporters Thursday that Iran may not have intentionally downed an unmanned U.S. surveillance drone. He said the public will "find out" about whether the U.S. intends to retaliate with a military strike.

"I find it hard to believe it was intentional," Trump said during a White House meeting with Canadian Prime Minister Justin Trudeau.

"I think they made a mistake, and I'm not just talking the country made a mistake. I think that someone under the command of that country made a big mistake," Trump said.

U.S. stocks briefly dipped to session lows after Trump said "you'll soon find out" when asked if the U.S. would strike Iran. They resumed their climb with his subsequent comments about Iran's intentions.

U.S. officials said earlier in the day that an Iranian missile had shot down the drone over the Strait of Hormuz, a shipping route through which much of the world's oil flows. Iran claimed that the drone was above its territory.

Speaker Nancy Pelosi called on U.S. allies to "recognize that we are not dealing with a responsible adversary" and that the international community should do everything to de-escalate.

"In light of the targeting of an unmanned U.S. drone by Iran, it is essential that we remain fully engaged with our allies, recognize that we are not dealing with a responsible adversary and do everything in our power to de-escalate," Pelosi said in a statement.

"This is a dangerous, high-tension situation that requires a strong, smart and strategic, not reckless, approach."

Talking with reporters, Trump repeated the claim that the drone was flying above international waters. But the president suggested that the incident may have been unintended and done by someone who was "loose and stupid." He declined to rule out talks with Tehran, saying that he would see what happens.

Trump declined to provide more specifics about a potential U.S. response.

Earlier Thursday, Trump tweeted "Iran made a very big mistake!"

Iranian state media first reported on the downing of the American military drone. The Iranian outlet Sepah News claimed the Islamic Revolutionary Guards shot down a U.S. "spy drone" over the southern province of Hormozgan.

Major Gen. Hossein Salami, who was the recently appointed to lead the Revolutionary Guard, told Iranian state TV that "Iran is not seeking war with any country, but we are fully prepared to defend Iran."

The U.S. and Iran have sparred in recent weeks over two attacks on oil tankers in the Persian Gulf region. Trump has accused Iran of being behind the attacks, which Iran has denied.

— CNBC's Natasha Turak contributed to this report from Dubai, Amanda Macias and Christina Wilkie contributed to this report from Washington.

WATCH: Trump remarks on possibility of U.S. strike