Security forces and demonstrators have been involved in clashes for more than eight months [Reuters]

The US has called on Bahrain to investigate the case of a prominent human rights activist who says he was beaten by security forces.

Opposition activists said that several security officers threw Nabeel Rajab, head of the Bahrain Centre for Human Rights, to the ground and beat him on the head, neck and back after a protest march on Friday.

Bahrain's interior ministry has denied those accounts, saying on its Twitter feed that police found Rajab "lying on the ground" and took him to the hospital for treatment.

The Sunni-led island kingdom, home to the US' largest navy fleet, has sought to crush anti-government demonstrations mounted by the country's Shia majority.

Officials from the US embassy in Manama met for about an hour on Saturday with Rajab, who had a cut beneath one eye and bruising on his face, a senior US official told the Reuters news agency on condition of anonymity.

"We are very concerned about this case," said the senior US official who spoke on condition of anonymity, saying that if an investigation found the Bahraini police used excessive force against him, those responsible should be punished.

State department 'concerns'

Victoria Nuland, US state department spokesperson, said in a written statement that embassy officials had raised Rajab's case with senior Bahraini officials and urged the government to carry out recommendations made by an independent commission that found Bahrain used excessive force in last year's crackdown.

"The United States is deeply concerned by continuing incidents of violence in Bahrain between police and demonstrators," she said.

"While the facts surrounding the violence that transpired remain in dispute, we strongly urge the Government of Bahrain to undertake a full investigation [of Rajab's case] to determine if excessive force was employed by police.

"In general we urge all demonstrators to refrain from acts of violence and for police and security forces also to avoid excessive use of force."

Bahrain launched a sweeping crackdown on anti-government protests last year that drew criticism internationally and from the state-sponsored Bahrain Independent Commission of Inquiry (BICI), which found detainees were systematically abused and in some cases tortured to death.

The events in Bahrain have posed a policy challenge for the US because of its naval presence there.

The US has said a $53m arms sale to Bahrain depends in part on the kingdom's response to the recommendations of the BICI, which issued its report on November 23.