The protesters demonstrated holding placards against Cameron at the central Colombo's main mosque after Friday prayers. They accused the British Prime Minister of being influenced by the pro-LTTE diaspora in Britain.
On the sidelines of the Commonwealth Heads of Government Meeting here last week, Cameron gave Sri Lanka an ultimatum to conduct a credible probe into the war crimes by March, failing which he would seek an international investigation.
He told reporters that his government would work with the UN Human Rights Council to urge an international investigation into alleged war crimes committed by Sri Lankan troops during the final phase of the war against the LTTE.
Yesterday, a Sri Lankan Buddhist nationalist group staged a protest in front of the UK's embassy here against Cameron's warning.
The British High Commission here was also presented with a written request to probe war crimes committed by British troops on quelling a rebellion in Sri Lanka during the colonial era.
The British rule in 1818 was accused of massacring the locals by the nationalist government ally, National Freedom Front's Buddhist monk clan, 'Ravana Balaya'.