LONDON - Four protesters were arrested after gaining access to the balcony of the Iranian embassy in London on Friday, police said, prompting a complaint from Tehran about security at the building.

"We were called at 4.20 pm (1620 GMT) to reports of four protesters on the balcony of the Iranian embassy in Princes Gate, Knightsbridge," a spokeswoman for London's Metropolitan Police said.

At around 6.40 pm (1840 GMT) all four men were arrested on suspicion of criminal damage and being unlawfully on diplomatic premises. "All four people have been taken to a central London police station. They remain there in custody," the spokeswoman said. It is understood the protesters did not manage to get inside the building.

Iranian foreign ministry spokesman Bahram Ghasemi said Tehran had lodged a strong protest with the British government over the incident, according to the IRNA state news agency.

The report said supporters of an "extreme cult" living in Britain were responsible.

Iran's deputy foreign minister Abbas Araghchi made his protest known to the British ambassador in Tehran, demanding "absolute protection of our diplomats in London and immediate dealing of the police with the attackers", IRNA said.

In a statement, a Foreign Office spokesman said: "The safety and security of diplomats and diplomatic missions in the UK is of paramount importance to us."

In 1980, six gunmen who supported a dissident Iranian group took over the Iranian embassy in London, taking more than two dozen hostages.

After a six-day siege, British special forces raided the building, killing five of the gunmen and arrested another. Two of the hostages also died.