Bahrain's foreign ministry insists that it respects citizens' right to hold peaceful protests, and that security forces only intervene when demonstrations become violent.

"The kingdom of Bahrain authorises the peaceful expression of opinion within the constitution and the law," it said in a statement issued late on Thursday in response to concerns expressed by the US State Department.

"The security forces exercise maximum restraint even though they are regularly the target of acts of violence," the ministry said. "But these forces reserve the right to take necessary measures in the face of any escalation in violence."

On Wednesday, the State Department had urged Bahrain to exercise restraint and allow peaceful protests. It also condemned the unrest that broke out in the Gulf island state over the last two weeks, as anti-government protesters launched a renewed campaign of demonstrations demanding increased rights.

"We are deeply concerned about the increase in violence in Bahrain," Victoria Nuland, a spokesperson for the State Department, said. 

"We condemn the use of violence in all its forms - whether against peaceful demonstrators or police and government institutions - and urge all parties to reject such actions," Nuland said in a statement.

"We call on the government of Bahrain to permit peaceful protest and to exercise maximum restraint in maintaining order, just as we call on all those demonstrating to do so peacefully," she said.