GENEVA (AFP) - Sri Lanka must launch an in-depth probe into claims that government troops killed 40,000 civilians during a 2009 offensive against Tamil Tiger rebels that ended its three-decade civil war, the UN Human Rights Council said on March 21.

The UN's top human rights forum passed a resolution pressing Colombo to "credibly investigate widespread allegations of extrajudicial killings and enforced disappearances". To date, it said, Sri Lanka has failed to "adequately address serious allegations of violations of international human rights law and international humanitarian law".

Lodged by the United States - whose embassy in Colombo was the scene of protests by pro-government activists on March 21 - the text was backed by nations in Europe, as well as Canada and India.

"The resolution does very clearly state that the international community knows an independent and credible investigation must go forward, and that's what's lacking," US ambassador to the council Eileen Chamberlain Donahoe told reporters.

"No determination has been made by the council members yet on whether an international probe is required, but what we're hoping for is a domestic, credible independent investigation that satisfies the people of Sri Lanka," she added.

The text also flagged concerns about continuing abuses including killings, torture and violations of freedom of expression, as well as breaches of the rule of law.

Sri Lanka's rights minister Mahinda Samarasinghe said it was "unacceptable".

"It is highly intrusive, is replete with misrepresentations and in its overall scope accentuates the negative and eliminates or is dismissive of the positive," he told the council, adding that it brushed aside Sri Lanka's domestic reconciliation efforts.

"The Sri Lankan conflict ended three years and 10 months ago. There are other ongoing conflicts and reported violations of rights, as we speak, in several parts of the world. Our concern is, why this preoccupation with Sri Lanka?"

Mr Samarasinghe won vocal backing from Pakistan's ambassador Zamir Akram.

"Sri Lanka needs to be given the time and the space to address those challenges in a comprehensive manner by completing its domestic reconciliation process. What it does not need is to be subjected by highly critical and intrusive decisions by this council," he told the council.

The UN estimates that some 40,000 people were killed in the final months Sri Lanka's civil war, mostly in indiscriminate shelling by government forces during a final onslaught against Tamil separatists.

Sri Lanka insists that no civilian was killed by its troops. During the civil war, which began in 1983, the rebels made suicide bombings their hallmark.

The council's resolution underlined that states "must ensure that any measure taken to combat terrorism complies with their obligations under international law, in particular international human rights law, international refugee law and international humanitarian law". India, home to its own Tamil community, has taken a tough stance on the issue.

"We note with concern the inadequate focus by Sri Lanka in fulfilling its commitments," said India's ambassador Dilip Sinha.

In what appeared to be a reaction to India's support of the resolution, Sri Lanka on March 21 said that it would repossess part of a strategic oil storage depot from a state-run Indian firm.

The council in Geneva passed the resolution by 25 votes to 13 - the very fact of holding the ballot underlining the controversy in a body that strives to work by consensus.

It welcomed Sri Lanka's efforts to rebuild war-damaged infrastructure, clear landmines and resettle the majority of people who were displaced during the civil war.

But it said that "considerable work lies ahead in the areas of justice, reconciliation and the resumption of livelihoods", and that all groups, including minorities, should be able to participate fully.

Human-rights campaigners hailed the resolution.

"UN member states have sent a clear signal to the Sri Lankan government that crimes of the past cannot simply be ignored, but need to be investigated and the perpetrators brought to justice," said activist Yolanda Foster of Amnesty International.