Bahrain arrested 29 people in the commercial district of the capital Manama on Friday as anti-government protesters marched in the city centre in defiance of a government ban, state media said late Friday.

Bahrain, where the US Fifth Fleet is based, has been in political turmoil since a protest movement dominated by majority Shia Muslims erupted in February 2011 demanding the Sunni-led monarchy enact democratic reforms.

The demonstration was organised by an opposition group called February 14, said Jasim Husain, one of the leaders of the main opposition group, Wefaq. It came two weeks after protesters and police clashed in the city centre for the first time since last year, following months of demonstrations in other parts of Manama and elsewhere in the country.

"Rioters hurled petrol bombs, iron rods and stones, endangering both the police and civilians in the area," the government Information Affairs Authority said in an emailed statement.

The government has taken a zero-tolerance approach to protests in the city centre, saying unrest in "vital commercial areas" could damage the economy.

The statement added that police "used only the necessary force to restore order," that the 29 people arrested would be referred to the public prosecutor. It said there would be an investigation to identify others involved in the protest.

"People should have the right to stage rallies in the capital. A rally on a Friday afternoon is not a big deal. It will not undermine the economy," said Husain.

In Bahrain, the weekend falls on a Friday.

The United States urged Bahrain this week to accelerate democratic change and hold talks with the opposition after a meeting in Geneva where Bahrain's foreign minister, Khalid Bin Ahmed Bin Mohammed Al-Khalifa, pledged "unprecedented reforms."