COLOMBO (AFP) - President Mahinda Rajapakse said on Saturday Sri Lanka must be trusted to conduct its own investigation into war crimes allegations and warned against international pressure on his regime's human rights record.

"People in glass houses must not throw stones," Rajapakse said in a press conference in Colombo where he is chairing a Commonwealth summit.

The three-day gathering has been overshadowed by allegations of war crimes by his troops at the end of an ethnic war in 2009.

British Prime Minister David Cameron had earlier given Rajapakse's regime until March to come up with credible results from its own investigation into the final stages of the war or else he would lead a push for the issue to be taken up by the United Nations.

Rajapakse, however, said Sri Lanka must be allowed to complete its own investigation in its own time.

"They have to trust us," he said.

"Pressure won't do anything. ... It's much better to wait rather than demand or dictate."

Asked about Cameron's ultimatum, Rajapakse said his critics "can say what they want, it is up to them."

He also insisted that Sri Lankan investigators who are currently looking into the finale of the war were "independent", saying a commission looking into the fate of thousands of missing people had already begun its work.

"We have appointed a commission for missing persons, they have already started their investigations," he said.

"So we have done what we can," he said.

"We will take our own time and investigate, you must wait," he added.

"It's just four years after the war."

He also reiterated that his administration had "nothing to hide" and that it had not received the credit due for ending the war, which raged for nearly four decades with some 100,000 lives lost.

"The end of the war itself has saved the lives of so many youths ... is it a crime to save their life?"