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A US envoy believed the president of Sri Lanka bore responsibility for an alleged 2009 massacre of Tamils, suggest cables obtained by Wikileaks.

The claim was

It comes as Sri Lanka's parliament was suspended after a scuffle between MPs over demonstrations in the UK against President Mahinda Rajapaksa's visit.

More protests are planned later in London outside the hotel where Mr Rajapaksa is thought to be staying.

The demonstrations have been blamed for the Oxford Union's decision to cancel a speech by Mr Rajapaksa planned for Thursday.

Thousands of Tamil civilians are estimated to have been killed during a military bombardment as the 26-year insurgency ended in May last year.

The US ambassador in Colombo, Patricia Butenis, said in a diplomatic cable sent on 15 January this year that President Rajapaksa and the former army commander, Sarath Fonseka, were largely responsible.

She said there seemed little hope of accountability given that there were no examples of a regime investigating its own troops for war crimes.

"In Sri Lanka this is further complicated by the fact that responsibility for many alleged crimes rests with the country's senior civilian and military leadership, including President Rajapaksa and his brothers and opposition candidate Gen Fonseka," Ms Butenis writes.

It is one of more than 250,000 classified American diplomatic cables, obtained by the Wikileaks website and released to several publications, including the Guardian and the New York Times.

On Thursday, parliament in the capital, Colombo, had to be suspended after several MPs tried to attack an opposition Sinhalese member.

Dr Jaylath Jayawardena was accused of instigating a protest by a large group of Tamil demonstrators at London's Heathrow Airport as President Rajapaksa arrived on Monday night.

Dinesh Gunawardena, a cabinet minister, called for an inquiry into the conduct of the United National Party MP.

Several government members then tried to assault Dr Jayawardena, who was protected by a few of his colleagues and some members of the ruling party.

Sri Lanka has repeatedly rejected international calls for an independent inquiry into the war against the Tamil Tigers.

At least 7,000 Tamil civilians were killed in a few days of bombardment when the military cornered the rebels in a small coastal strip in May last year, according to the UN.

Other estimates put the death toll as high as 20,000. Both sides have been accused of crimes against humanity.

The former army chief, Sarath Fonseka, said last year during his failed campaign for the presidency that military decisions had been taken in the final days of the war without his knowledge.

These included the president's brother, Defence Secretary Gotabhaya Rajapaksa, allegedly ordering Tamil Tiger rebel leaders to be shot dead as they tried to surrender, Mr Fonseka claimed.

The Sri Lankan government said they were shot by other insurgents.

Mr Fonseka led troops to victory last year over the Tamil Tigers, but fell out with the president when he stood unsuccessfully against him in polls; he was charged with corruption and jailed.

Meanwhile, Colombo dismissed the authenticity of footage broadcast by the UK's Channel 4 News, purportedly showing Tamil prisoners being killed.

Channel 4 said the video - apparently showing trussed-up male and female prisoners being shot dead amid taunts from onlookers - was taken shortly before the Tamil Tigers' defeat.