Two protesters scaled the roof of Bahrain's embassy in London on Monday and unfurled a banner in support of two Shi'ite Muslim activists jailed in the Gulf Arab country that has been hit by political unrest before next weekend's Grand Prix motor race.

Bahrain's Foreign Ministry described the men as "terrorists" after they climbed to the top of the embassy in central London in the middle of the day Reuters reported.

It called on Britain to remove the men from the roof and to take full responsibility for protecting the embassy building and diplomats. British police said they were on the scene and had closed part of Belgrave Square, where the embassy is located.

One of the protesters sent photographs of their rooftop action over social media from an account identifying him as Moosa Abd Ali.

The other man, reported to be Ali Mushaima, the son of jailed Shi'ite dissident leader Hassan Mushaima, told local media they were protesting against human rights violations in Bahrain and over the decision by Formula One to hold its race there this weekend.

Their banner showed pictures of Mushaima and Abdulhadi al-Khawaja, a leading figure in protests against the Sunni ruling family of Bahrain that were crushed last year.

Three teenagers were wounded later that day at a rally in Manama after the funeral of a man shot during a protest two weeks ago.