Iran's Revolutionary Guard said Thursday it shot down a U.S. drone amid heightened tensions between Tehran and Washington over its collapsing nuclear deal.

A U.S. official said the drone has been shot down in international airspace over the Strait of Hormuz by an Iranian surface-to-air missile.

Speaking on condition of anonymity, the official said the drone was a U.S. Navy MQ-4C Triton. No further details were immediately available, including the time of the shoot-down.

CENTCOM later said in a statement that a U.S. surveillance aircraft was shot down by Iranian surface-to-air missile over the Strait of Hormuz, rejecting claims that the aircraft was over Iran.

Late Thursday Foreign Minister Mohammad Javad Zarif announced that parts of the drone had been recovered in Iranian territorial waters, as Tehran moved to bring the incident before the United Nations.

"We don't seek war, but will zealously defend our skies, land & waters," Zarif said.

He said earlier on Twitter that the drone had taken off from the United Arab Emirates.

"At 00:14 U.S. drone took off from UAE in stealth mode & violated Iranian airspace. It was targeted at 04:05 at the coordinates (25°59'43"N 57°02'25"E) near Kouh-e Mobarak. We've retrieved sections of the US military drone in OUR territorial waters where it was shot down," Zarif tweeted.

Following the incident, President Donald Trump tweeted: "Iran made a very big mistake!"

Trump, however, changed his tone later in the day to indicate he meant Iran made a mistake, as in an unintentional action.

"I find it hard to believe it was intentional," Trump said at the White House in comments that appeared to downplay the incident, despite soaring tension in the strategic Strait of Hormuz area.

"I have a feeling that it was a mistake made by somebody who should not have been doing," he said.

Asked how the U.S. will respond, Trump answered: "You'll find out."

The shootdown of the drone comes after the U.S. military previously alleged Iran fired a missile at another drone last week that responded to the attack on two oil tankers near the Gulf of Oman. The U.S. blames Iran for the attack on the ships, which Tehran denies.

The attacks come against the backdrop of heightened tensions between the U.S. and Iran following President Donald Trump's decision to withdraw from Tehran's nuclear deal with world powers a year ago. The White House separately said it was aware of reports of a missile strike on Saudi Arabia amid a campaign targeting the kingdom by Yemen's Iranian-allied Houthi rebels.

Iran recently has quadrupled its production of low-enriched uranium and threatened to boost its enrichment closer to weapons-grade levels, trying to pressure Europe for new terms to the 2015 deal.

In recent weeks, the U.S. has sped an aircraft carrier to the Mideast and deployed additional troops to the tens of thousands already in the region. Mysterious attacks also have targeted oil tankers as Iranian-allied Houthi rebels launched bomb-laden drones into Saudi Arabia.

All this has raised fears that a miscalculation or further rise in tensions could push the U.S. and Iran into an open conflict, some 40 years after Tehran's Islamic Revolution.

Iran's paramilitary Revolutionary Guard, which answers only to Supreme Leader Ayatollah Ali Khamenei, said it shot down the drone Thursday morning when it entered Iranian airspace near the Kouhmobarak district in southern Iran's Hormozgan province. Kouhmobarak is some 1,200 kilometers (750 miles) southeast of Tehran and is close to the Strait of Hormuz.

Iran's state-run IRNA news agency, citing the paramilitary Revolutionary Guard, identified the drone as an RQ-4 Global Hawk.

Capt. Bill Urban, a U.S. Central Command spokesman, declined to comment when asked if an American drone was shot down.

However, he told The Associated Press: "There was no drone over Iranian territory."

Meanwhile, White House spokeswoman Sarah Sanders said Trump had been "briefed on the reports of a missile strike in the Kingdom of Saudi Arabia."

"We are closely monitoring the situation and continuing to consult with our partners and allies," Sanders said.

The Houthi's Al-Masirah satellite news channel claimed the rebels targeted a power plant in Jizan, near the kingdom's border with Yemen, with a cruise missile. Saudi state media and officials did not immediately report a missile strike Thursday.

A Saudi-led coalition has been battling the Houthis since March 2015 in Yemen, the Arab world's poorest nation now pushed to the brink of famine by the conflict. In recent weeks, the Houthis have launched a new campaign sending missiles and bomb-laden drones into Saudi Arabia.