Three Iranian Islamic Revolutionary Guard Corps’ vessels “attempted to impede” of a British oil tanker in the Persian Gulf on Wednesday, according to a statement by the U.K. government.

The oil tanker British Heritage, under escort by U.K. Royal Navy frigate HMS Montrose due to a recent increase in tensions in the region, was reportedly entering the Strait of Hormuz between the Persian Gulf and the Gulf of Oman when it was approached by the IRGC vessels.

The U.K. Defense Ministry said in a statement that the HMS Montrose was “forced to position herself between the Iranian vessels and British Heritage and issue verbal warnings to the Iranian vessels, which then turned away,” according to The Guardian.

CNN reported on Thursday that a U.S. aircraft recorded video footage of the event, but that the footage had not yet been released.

Iran has denied attempting to stop the British vessel.

The incident occurred a week after the Iranian oil tanker Grace 1 was seized by the United Kingdom off the coast of Gibraltar on suspicion of transporting oil to Syria in violation of E.U. sanctions.

Chief of Staff for the Armed Forces of the Islamic Republic of Iran Maj. Gen. Mohammad Bagheri said the seizure was “based on “fabricated excuses,” and warned that it “will not be unanswered, and when necessary, Tehran will give the appropriate answer.”

His remarks were bolstered by Iranian President Hassan Rouhani, who accused the United Kingdom on Wednesday of “initiating insecurity” and warned “you shall grasp the consequences of it later on.”

Last month, Iran shot down a U.S. drone above the Strait of Hormuz, after which U.S. President Donald Trump came close to authorizing retaliatory strikes against the Islamic Republic, calling them off at the last moment.

Also on Wednesday, the International Atomic Energy Agency confirmed Iran is enriching uranium to 4.5 percent purity, above the 3.67 percent limit agreed upon in the Joint Comprehensive Plan of Action in 2015.