Iran is accusing the United States of "a very dangerous and provocative act" and is urging the international community to demand that the U.S. end its unlawful actions and drone spying.

Iran's U.N. Ambassador Majid Takht Ravanchi says a U.S. drone despite repeated radio warnings entered into Iranian airspace after conducting "an overflight through the Strait of Hormuz to Chabahar port in a full stealth mode as it had turned off its identification equipment and engaged in a clear spying operation."

Ravanchi said in a letter to the U.N. secretary-general and the Security Council obtained late Thursday that according to Iran's Armed Forces General Staff after the "U.S. unmanned aircraft system" entered Iranian airspace and its air defense system targeted "the intruding aircraft."

He said Iran acted under Article 51 of the U.N. Charter which allows military action in self-defense.

Earlier, President Donald Trump played 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.

During a bilateral meeting with Canadian Prime Minister Justin Trudeau, Trump said, "Iran made a big mistake. This drone was in international waters clearly, we have it all documented, it's documented scientifically not just words and they made a very bad mistake."

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.

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.

The U.S. military's Central Command (CENTCOM) confirmed Thursday that the downed aircraft was a RQ-4A Global Hawk High-Altitude Long Endurance (HALE) Unmanned Aircraft System (UAS), which it said "provides real-time intelligence, surveillance and reconnaissance missions (ISR) over vast ocean and coastal regions."

It is the largest drone in the U.S. military fleet and is designed to fly at much higher altitudes than other unmanned aircraft – capable of reaching altitudes more than 10 miles over the Earth's surface.

Earlier this week, Air Force Gen. Paul Selva, Vice Chair of the U.S. Joint Chiefs of Staff, told the Defense News website that the U.S. would not take military action against Iran without broad international backing, "with one specific caveat: If the Iranians come after U.S. citizens, U.S. assets or U.S. military, we reserve the right to respond with a military action. They need to know that, it needs to be very clear."

The incident comes after the Trump Administration decided Monday to deploy 1,000 additional troops to the Middle East. 

The country's military leader reportedly said Iran does not want a conflict, but is "completely, and totally ready and prepared for war." 

(The Associated Press, CBS News contributed to this report.)