Undated photograph shows the Mesdar, a British-operated oil tanker in Fawley

This undated photograph shows the Mesdar, a British-operated oil tanker in Fawley, Britain. The ship was boarded by armed guards and then allowed to go on its way, according to reports Friday. A second tanker was seized by Iran.

NEW YORK — Iran’s Revolutionary Guard Corps seized a British oil tanker in the Strait of Hormuz amid soaring tensions in one of the world’s critical energy chokepoints. Brent climbed more than 1% on the news.

A spokesperson for the British government said it was urgently seeking further information and assessing the situation following reports of an incident in the gulf. An official with the U.S. National Security Council said it was aware of the reports and vowed to work with allies and partners against Iran’s “malign behavior.”

It was the second Iranian move against a U.K. ship in just more than a week. On July 11, the British navy intervened to stop Iran from blocking a commercial oil tanker leaving the Persian Gulf. That followed an incident in early July when U.K. forces seized a tanker off Gibraltar that was suspected of carrying Iranian oil to Syria. Iran denied the vessel was heading to Syria and has since vowed to retaliate.

The tit-for-tat actions signal greater instability and potential conflict in a region where one-third of the world’s seaborne crude and fuels pass through. The U.S. and Iran have been locked in a standoff over American sanctions on Iranian oil following President Donald Trump’s withdrawal from the 2015 nuclear accord last year.

“These incidents in isolation are not especially alarming,” former U.S. National Security Adviser Susan Rice said at a conference in Aspen, Colo. But, she added, “In the aggregate they are, given that we’re dealing with players that have little interest in deescalating.”

Recent weeks have seen a spate of attacks on oil tankers and other flare ups in the gulf region. On Thursday, the U.S. said it downed an Iranian drone that was endangering the naval ship USS Boxer, a claim Iran has rejected. In June, Trump said he called off a retaliatory strike on Iran following Tehran’s move to shoot down an American drone.

On Friday, the Swedish owner of the Stena Impero said it “was approached by unidentified small crafts and a helicopter during transit of the Strait of Hormuz while the vessel was in international waters” at about 4 p.m. London time. “We are presently unable to contact the vessel which is now heading north towards Iran.”

The 49,683 deadweight ton tanker, which has 23 workers aboard and typically carries refined products, was last heading to Jubail, Saudi Arabia, according to ship-tracking data compiled by Bloomberg.

Bloomberg News