Iran on Friday denied U.S. President Donald Trump's assertion that the U.S. Navy has destroyed one of its drones, saying all of its unmanned planes were accounted for, amid growing international concern that both sides could blunder into a war in the Gulf. 

In the latest episode to test nerves around the strategic waterway, Trump said on Thursday the USS Boxer, an amphibious assault ship, destroyed an Iranian drone in the Strait of Hormuz after the aircraft threatened the vessel. 

"The Boxer took defensive action against an Iranian drone which had closed into a very, very near distance, approximately 1,000 yards (914 meters), ignoring multiple calls to stand down and was threatening the safety of the ship and the ship's crew. The drone was immediately destroyed," said Trump during an event at the White House.

Iran, however, 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 spokesperson, was quoted as saying by the semi-official Tasnim news agency. 

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

A U.S. official, speaking on condition of anonymity, said the drone on Thursday was brought down through electronic jamming.

Caution from both sides

Gulf tensions are high, with fears the United States and Iran could stumble into war. But despite tough talk on both sides, Washington and Tehran have shown restraint.

German Chancellor Angela Merkel said that she was concerned about the situation in the Gulf. 

"Of course I'm concerned. You can't look at this region without being concerned at the moment," Merkel told a news conference. "Every opportunity for diplomatic contact should be attempted to avoid an escalation." 

In the latest development in a related standoff between Iran and Britain, Gibraltar's supreme court granted a 30-day extension to allow authorities to detain the Iranian oil tanker Grace 1 until August 15, the Gibraltar Chronicle reported. 

Iran has vowed to respond to what it calls Britain's "piracy" over the seizure of the vessel. 

The tanker was seized earlier this month by British Royal Marines off the coast of the British Mediterranean territory on suspicion of violating sanctions against Syria. 

The United States has blamed Iran for a series of attacks since mid-May on shipping around the Strait of Hormuz, the world's most important oil artery. Tehran rejects the allegations. 

Iran in June shot down a U.S. military surveillance drone in the Gulf with a surface-to-air missile, saying the drone was in its airspace, while Washington said it was in international skies. 

The increased use of drones by Iran and its allies for surveillance and attacks across the Middle East is raising alarms in Washington. 

Iran's Revolutionary Guards said in a statement they would release images to disprove Trump's contention that the U.S. Navy had destroyed a drone. 

"Soon, images captured by the Guards drones from the U.S. warship Boxer will be published to expose to world public opinion as lies and groundless the claim," the Guards said.

(With input from Reuters and AP)

(Cover: Amphibious assault ship USS Boxer during Exercise Ssang Yong, March 7, 2016. /VCG Photo)