Iran's foreign ministry spokesman on Friday called on the United Kingdom to release the country's oil tanker which the British Royal Marines seized last week.
In an interview with Iran's state news agency, Abbas Mousavi said that there would be "consequences" and said that foreign powers should "leave the region".
Last week British Royal Marines boarded an Iranian tanker, Grace 1, off Gibraltar and seized it on suspicion that it was breaking EU sanctions by taking oil to Syria.
The UK, meanwhile, announced on Friday that it is sending a second warship to the Persian Gulf. The HMS Duncan, currently stationed in the Mediterranean, should reach the area next week to lend support to the HMS Montrose which is coming off the end of its mission.
"As part of our long-standing presence in the Gulf, HMS Duncan is deploying to the region to ensure we maintain a continuous maritime security presence while HMS Montrose comes off task for pre-planned maintenance and crew changeover," a statement from Britain's Ministry of Defence stated.
"This will ensure that the UK, alongside international partners, can continue to support freedom of navigation for vessels transiting through this vital shipping lane," it added.
It comes two days after the UK said that three Iranian vessels tried to block a British-flagged oil tanker in the Strait of Hormuz. The UK defence secretary, Penny Mordaunt, said in a statement on Thursday that the government was "concerned by this action" and urged "the Iranian authorities to de-escalate the situation".
Mordaunt thanked the Royal Navy for ensuring the "safe passage" of the vessel British Heritage through the Strait of Hormuz.
The navy's HMS Montrose had issued "verbal warnings to the Iranian vessels" a British government spokesman said in a statement.
Earlier on Wednesday, Iranian President Hassan Rouhani said Britain would face "consequences" over the seizure of the Iranian tanker.
Iranian foreign minister Javad Zarif said on Monday that the seizure of Iran's tanker had set "a dangerous precedent".
Tensions between Iran and the United States and its allies have risen sharply since Washington stepped up economic sanctions against Iran and moved to bring the country's oil exports to zero as part of a "maximum pressure" policy to make Iran halt actions that it said undermined regional security.
Iran has responded to the sanctions by starting to breach limits put on its nuclear activities under a 2015 deal with world powers.
Oil tankers were attacked in waters near Iran's southern coast in May and June, for which the United States blamed Iran. Tehran denied any involvement.
Last month, Iran shot down a U.S. drone near the Strait of Hormuz, prompting President Donald Trump to order retaliatory air strikes, only to call them off.
U.S. officials, speaking on the condition of anonymity, said Wednesday's incident happened as British Heritage was at the northern entrance of the Strait of Hormuz.
"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," one of the officials said.
"It was harassment and an attempt to interfere with the passage," the other official said.
The United States hopes to enlist allies over the next two weeks or so in a military coalition to safeguard strategic waters off Iran and Yemen, Marine General Joseph Dunford, the chairman of the Joint Chiefs of Staff, said on Tuesday.