Britain's Prime Minister David Cameron made an historic visit Friday to Sri Lanka's former warzone, stealing the spotlight from a Commonwealth summit after the host, President Mahinda Rajapakse, warned against passing judgement on his country's past.

Only hours after the summit opened in Colombo, Cameron flew into the northern Jaffna region where some 100,000 people lost their lives in fighting between Tamil rebels and troops from the majority Sinhalese government.

Several women who lost relatives during the war tried to hurl themselves in front of Cameron's motorcade as he became the first foreign leader to visit Jaffna since the former British colony gained independence in 1948.

Clutching photos of their missing loved ones, they screamed "We Want Justice" before the premier sped away.

He later toured the offices of a Tamil newspaper whose printing presses have been torched several times, including in April this year, and which has lost five staff in attacks since Rajapakse came to power in 2005.

"This is going to make a very lasting impression on me. That is something you don't forget," Cameron told journalists at the Uthayan ("The Sun") daily where the portraits of slain staff line the walls.

"But it's only when you see it with your own eyes, it really brings home just how much you're suffering."

M.V Kaanamylnathan, the paper's editor, said Cameron visit was a chance to publicise the region's plight.

"Everyone is pretending that everything is okay, that Tamils have equal rights but it's not true," he told AFP in Jaffna.

"This needs to be told to the international world."

The landmark visit overshadowed the start of a three-day summit which was meant to be a chance for Rajapakse, a Sinhalese nationalist who oversaw the crushing of Tamil Tiger rebels in 2009, to showcase Sri Lanka's revival.

But after refusing to bow to demands for an independent investigation into the end of the conflict, he has been confronted by a public relations disaster, including a string of boycotts.

Cameron flew out of Colombo shortly after Rajapakse said in an opening speech warned his fellow leaders of trying to impose their own "bilateral agendas".

"If the Commonwealth is to remain relevant to its member countries, the association must respond to the needs of its people and not turn into a punitive or judgemental body," he said in a speech ahead of the formal opening of the summit by Britain's Prince Charles.

Since the war, the economy has enjoyed growth rates of up to 8.2 percent and more than one million tourists visited Sri Lanka last year -- a new record.

But the legacy of the war continues to poison Rajapakse's relations with the international community.

Canada's Prime Minister Stephen Harper was the first to announce a boycott after his government said the summit was akin to "accommodating evil" while his Mauritian counterpart Navin Chandra Ramgoolam -- due to host the next one -- is also refusing to attend.

Even India's Prime Minister Manmohan Singh is staying away, preferring to antagonise a neighbour rather than offend Tamil voters ahead of next year's elections.

The agenda for the three-day summit includes sessions on debt restructuring and climate change.

But Rajapakse spent the build-up fending off allegations that his troops were responsible for the death of some 40,000 Tamil civilians in the final weeks of the war.

During an impassioned speech, the 67-year-old leader said his regime deserved credit for ending the conflict.

"We asserted the greatest human right -- the right to life," he said.

"In the last four years there has not been one single terrorism-related incident in Sri Lanka."

The Jaffna peninsula, home to around 800,000 Tamils, was the main battleground of the war and its towns and villages are now littered with shelled-out buildings. Some 30,000 people still live in refugee camps.

Although provincial elections were held in Jaffna in September, they fell well short of Tamil demands for more autonomy.

Cameron spoke with the new chief minister of Jaffna, C. V. Wigneswaran, for about 30 minutes at the town's library as dozens of women who still don't know what happened to their loved ones demonstrated outside.

At the last summit in 2011 in Perth, Commonwealth leaders drew up a charter of common values which committed members to respecting human rights.

Australian Prime Minister Tony Abbott, the Commonwealth's outgoing chair, acknowledged Sri Lanka was emerging from a troubled past and said its people could take heart from how South Africa had come through darker times.

"Sri Lanka's willingness to host this Commonwealth shows its commitment to democratic pluralism and freedom based on law and ought to reassure all its citizens that just as today is better than yesterday, tomorrow will be better than today," he said.

"So we are here to praise as much as to judge."

Prince Charles, who is representing his mother Queen Elizabeth II, said the Sri Lankan people had "confronted great adversity," as he also recalled the devastating impact on the island of the 2004 tsunami.