Iran on Friday denied President Donald Trump's assertion that the U.S. Navy has destroyed one of its drones, saying all of its unmanned planes were safe, but there was no sign of a major Gulf escalation despite fears both sides could blunder into war.

Trump said Thursday that a U.S. Navy ship had destroyed an Iranian drone in a "defensive action," escalating already high tensions in the oil-rich Gulf region.

Iran dismissed the report.

"All drones belonging to Iran in the Persian Gulf and the Strait of Hormuz ... returned safely to their bases after their mission of identification and control," Abolfazl Shekarchi, a senior armed forces spokesman, was quoted as saying by the semi-official Tasnim news agency.

"And there is no report of any operational response by USS Boxer."

The USS Boxer, an amphibious assault ship, took down the drone in the Strait of Hormuz earlier Thursday, Trump claimed.

The Boxer is part of a group of Navy ships that was in the strait, located between the Persian Gulf and the Gulf of Oman, as part of an increased U.S. military presence in the region.

Twenty percent of the world's crude oil passes through the Strait of Hormuz.

The incident came four weeks after Iran shot down a U.S. surveillance drone flying over international airspace the same area, in what American officials at the time called an "unprovoked attack."

And it came hours after Iran's Revolutionary Guard seized a foreign tanker it accused of smuggling oil.

During an event at the White House, Trump said, "The Boxer took defensive action against an Iranian drone, which had closed into a very, very near distance, approximately 1000 yards, ignoring multiple calls to stand down and was threatening the safety of the ship and the ship's crew."

"The drone was immediately destroyed," Trump said.

The president called the drone's approach toward the Boxer "the latest of many provocative and hostile actions against vessels operating in international waters."

He said the United States "reserves [the] right to defend our personnel, our facilities, and interests and calls upon all nations to condemn Iran's attempts to disrupt freedom of navigation and global commerce."

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"I also call on other nations to protect their ships as they go through the Strait and to work with us in the future," Trump said.

A U.S. defense official would not say how the drone was brought down when asked by CNBC.

The USS Boxer is equipped with the Phalanx CIWS — close-in weapon system — for defense against threats including anti-ship missiles and helicopters.

The ship also is armed with short-range anti-ship missiles and non-kinetic systems that could be capable of targeting a drone.

The Pentagon, in a statement issued after the president spoke, said, "At approximately 10 a.m. local time, the amphibious ship USS Boxer was in international waters conducting a planned inbound transit of the Strait of Hormuz."

"A fixed wing unmanned aerial system (UAS) approached Boxer and closed within a threatening range. The ship took defensive action against the UAS to ensure the safety of the ship and its crew," the Pentagon said.