DUBAI: Five bombs exploded in the heart of the Bahraini capital Manama on Monday, killing two people, officials said, in rare attacks targeting civilians during the 21-month-old uprising against the kingdom's US-backed rulers.

The blasts, one outside a cinema, could be a sign that radical elements of the opposition are escalating violence.

They took place days after the government said it had banned all rallies and opposition gatherings to ensure public safety.

The victims were Asian street cleaners and one died after kicking a device which then blew up, said the Interior Ministry.

It said the bombs were home-made and described the blasts as “terrorist acts” - its term for attacks by opposition activists.

Police have been targeted by explosions several times this year, as the government has stepped up efforts to quell the uprising that has simmered since democracy protests broke out in early 2011.

But bombs targeting civilians are rare in the Gulf nation, where the Sunni Muslim Khalifa dynasty rules over a majority Shi'ite population. The kingdom hosts the US Fifth Fleet, which patrols oil shipping lanes in the Gulf region.

The explosions on Monday took place between 4.30 am and 9.30 am (0130 and 0630 GMT) in the Qudaibiya and Adliya districts of Manama, the BNA agency said, citing a police official. It described the explosives as “locally made bombs”. A third Asian worker was wounded, it said.

Washington has called on Manama to begin dialogue on democratic reforms with the opposition but criticism has been offset by its support for a country that plays a key role in U.S. efforts to challenge Iranian influence in the region.

The United States and Gulf allies fear Iran's nuclear energy programme is a front for developing nuclear weapons, a charge Tehran denies. Iran, a Shi'ite power, also denies accusations from Manama of fomenting the unrest in Bahrain.

Thirty-five people were killed in Bahrain during protests in February and March 2011 and the two months of martial law that followed.

But almost daily clashes have continued since between protesters and riot police in Shia districts.

Activists and rights groups say nearly 50 civilians have been killed in clashes with police since the end of martial law in June last year, while the authorities say two policemen have died including one killed by a bomb attack last month.

Opposition politician Matar Matar of Shi'ite party Wefaq said he doubted opposition activists were behind Monday's attacks, noting that leading Shi'ite clerics had called on followers to avoid escalating the conflict with the government.

He suggested the police or military may have been responsible, or a rogue unit.

“This incident is strange - why would anyone target workers?” he said. “I'm worried that police and military are losing control of their units or it is (preparation) before declaring martial law.”

The rallies ban announced last week was condemned by Amnesty International as a violation of the right to freedom of expression and peaceful assembly.