Iran's Revolutionary Guards denied on Thursday that they had impeded a British oil tanker in the Strait of Hormuz, the force's Sepah news agency said.

“There has been no confrontation in the last 24 hours with any foreign vessels, including British ones,” the Revolutionary Guards said in a statement.

Britain said on Thursday three Iranian boats had attempted to “impede the passage” of a British oil tanker in Gulf waters, forcing UK warship HMS Montrose to intervene.

The Guards' statement said that if they were ordered to seize foreign vessels they would do so "immediately, decisively and speedily". The incident follows the detention of an Iranian oil tanker by Britain on July 4 off the coast of Gibraltar, a tiny British overseas territory on Spain's southern tip.

The 330 metre Grace 1 tanker, capable of carrying two million barrels of oil, was halted by police and customs in Gibraltar with the aid of a detachment of British Royal Marines.

Iran condemned the detention as an “illegal interception”, but Gibraltar officials said that the cargo was believed to be destined for Syria, which is subject to European sanctions.

Iranian President Hassan Rouhani warned Britain on Wednesday of the “consequences” of what he described as “a foolish act”.

“I point out to the British that you initiated insecurity (on the seas) and you shall grasp the consequences of it later on,” Rouhani said in comments to the cabinet broadcast by state TV.

On Monday, Iran's defence minister had vowed to respond to Britain's move. Calling the tanker seizure an act of maritime piracy, Brigadier-General Amir Hatami said it "will not be tolerated by us and will not go without a response".

The secretary of Iran's Expediency Council, a key advisory and arbitration body, warned that if Britain failed to release the tanker Iran would be forced to take tit-for-tat action.

“If Britain does not release the Iranian oil tanker, the relevant authorities will be duty-bound to take reciprocal action and seize a British oil tanker,” said council secretary Mohsen Rezai.

The incident follows a spike in Iranian-US tensions in recent weeks, with Washington blaming Tehran for multiple attacks on tanker ships, and the Islamic republic shooting down an American surveillance drone.

It also comes as Europe mulls how to respond to Tehran breaching the uranium enrichment limit it agreed to under a landmark 2015 nuclear deal abandoned by the United States.