Britain's David Cameron put Sri Lanka on notice Saturday to address allegations of war crimes within months or else he would lead a push for action at the United Nations.

Speaking at a troubled Commonwealth summit in Colombo, the British premier warned his hosts that pressure over alleged abuses at the end of Sri Lanka's ethnic conflict was not about to go away.

He also told of how he had "frank" exchanges with Sri Lankan President Mahinda Rajapakse after he returned from a historic visit to the war-torn Jaffna region.

"The Sri Lankan government needs to go further and faster on human rights and reconciliation," Cameron told a press conference.

"I accept it takes time but I think the important thing is to get on the right track.

"This issue is not going to go away, it's an issue of international concern."

The UN and rights group say as many as 40,000 civilians may have been killed in the final stages of the civil war in May 2009 when Tamil Tiger rebels were routed.

However, Rajapakse has denied any civilians were killed and has also blocked all calls for an independent probe into claims of war crimes committed by government forces against the Tamil population in the Jaffna region.

Cameron said Rajapakse wanted more time to address the claims but put him on notice to deliver by March or else he would push for an international investigation through the auspices of the UN human rights council.

"Let me be very clear, if an investigation is not completed by March, then I will use our position on the UN Human Rights Council to work with the UN Human Rights Commission and call for a full, credible and independent international inquiry."

Cameron upstaged the first day of the three-day meeting on Friday by travelling to the Jaffna region which bore the main brunt of the 37-year civil war, meeting with local ethnic Tamils who lost loved ones or were left homeless.

He was the first foreign leader to visit Jaffna since Sri Lanka, a former British colony, gained independence in 1948.

While Sri Lanka had hoped the summit would showcase its revival since troops from the mainly Sinhalese government crushed the Tamil Tigers in 2009, Cameron's visit and boycotts by several leaders have torpedoed its strategy.

In a sign of Sri Lanka's anger at Cameron's visit, a senior minister said Saturday that the Commonwealth "should not be an international policeman".

"No country should be allowed to impose their thinking on another country," Irrigation Minister Nimal Siripala de Silva told reporters.

"We want the president to uphold the principle of non-interference" in sovereign affairs.

"We are not economically strong but we have our national pride."

Cameron received an emotional reception in Jaffna from locals who were desperate to tell him of their plight during the war and in its aftermath.

During his tour, Cameron met the editor of a newspaper whose printing presses have been torched several times, including in April. The same paper has lost five staff in attacks since Rajapakse came to power in 2005.

The desperation of locals was underlined when two women tried to hurl themselves in front of his convoy, clutching pictures of loved ones who were killed in the conflict which claimed more than 100,000 lives.

Cameron also spoke with elderly women who have had to live in shanty homes since the fighting ended in 2009.

Cameron held 45 minutes of talks late Friday with Rajapakse after his return to Colombo.

Asked about his meeting with Rajapakse, Cameron said "very strong views were expressed on both sides".

"Of course not everything I said was accepted," he added.

According to a statement from Rajapakse's office, the president asked Cameron to give Sri Lanka "more time to overcome all major challenges".

The meeting was likely to have added to Rajapakse's sense of anger and frustration after the leaders of Canada, India and Mauritius all stayed away.

Late Friday, Mauritian Prime Minister Navin Chandra Ramgoolam said his country was withdrawing as host of the 2015 Commonwealth summit.

"I have made it perfectly clear that human rights are more important than hosting a Commonwealth summit, regardless of its importance," Ramgoolam said.

Since the war, Sri Lanka's economy has enjoyed growth rates of up to 8.2 percent and major infrastructure projects such as a new $350 million highway linking Colombo to the main airport bear testimony to its revival.

The summit is meant to be focusing on issues such as poverty reduction and climate change but press conferences have been dominated by questions over alleged rights abuses by Sri Lankan forces.

The leaders are due to shift from the main conference venue in downtown Colombo on Saturday and will instead gather behind closed doors at a deluxe resort hotel on the outskirts of the capital.

Source: Wire Reports