Three Iranian boats tried to impede a British oil tanker in the Gulf on Wednesday, the United Kingdom government claimed. The incident took place while commercial vessel British Heritage was trying to pass through the Strait of Hormuz, The Guardian reported.

“Contrary to international law, three Iranian vessels attempted to impede the passage of a commercial vessel, British Heritage, through the strait of Hormuz,” the government said in a statement. It added that the British warship, HMS Montrose, was forced to position itself between the Iranian vessels and the oil tanker, and issue verbal warnings to the Iranian boats. “We are concerned by this action and continue to urge the Iranian authorities to de-escalate the situation in the region,” the statement added.

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The Iranian Revolutionary Guards rejected Britain’s claims. But a US surveillance aircraft recorded a video of the incident, CNN reported.

Unidentified US defence officials said the incident occurred at the northern entrance of the strait of Hormuz, Reuters reported. “The Royal Navy HMS Montrose, which was also there, pointed it guns at the boats and warned them over radio, at which point they dispersed,” the officials said. “It was harassment and an attempt to interfere with the passage.”

On Wednesday, Iranian President Hassan Rouhani had warned the UK of consequences after Britain seized an oil tanker bound for Syria off the coast of Gibraltar last week. The tanker is still in British custody.

Tensions between Iran and the United States have steadily increased since last month, when Tehran shot down an American spy drone over the Strait of Hormuz. While Iran claimed the drone had violated its airspace, the US maintained it was shot down over international waters. The incident came days after the United States accused Iran of attacking two of its oil tankers in the Gulf of Oman on June 13.