* Rights council hears country's presidential envoy
* Critics said falling for Tamil Tiger lies
* Pillay "used unsubstantiated evidence"
By Robert Evans
GENEVA, Feb 27 (Reuters) - Sri Lanka accused the U.N. human rights chief on Wednesday of being biased against it for criticising alleged killings of former Tamil Tiger independence fighters and political dissenters and journalists.
In a speech to the U.N. Human Rights Council, a senior official from Colombo also asserted that Western countries strongly critical of the country's record had fallen prey to lies spread by former members of the Tamil Tiger movement.
U.N. High Commissioner for Human Rights Navi Pillay, the official said, lacked "objectivity and impartiality" in reports to the council and her comments on Sri Lanka were based on "unsubstantiated evidence."
The official, presidential envoy on human rights Mahinda Samarasinghe, was speaking as the United States and European countries urged the 47-nation body to agree to instruct Sri Lanka to cease what they call rights abuses.
His sharp comments on Pillay, a former high court judge from South Africa, clearly reflected concern in Colombo - which is to host a summit of former British Commonwealth countries this year - at the prospect of fresh action by the council.
Non-governmental rights organisations, including a Geneva-based "rule of law" group, the International Commission of Jurists, are already campaigning for the 54-nation Commonwealth to cancel the high-profile gathering.
Last March the council, which is separate from Pillay's office, passed a resolution calling on Sri Lanka to ensure that government troops who committed war crimes near the end of the war against Tamil rebels were brought to justice.
That resolution was, like the latest now being prepared, brought by the United States and backed by a small majority of the council including India, Britain and other Commonwealth member countries as well as the 27-nation European Union.
Rights groups say the Sri Lankan military killed thousands of ethnic minority Tamil civilians in the shrinking territory held by rebels of the Liberation Tigers of Tamil Eelam just before their defeat in May 2009.
An expert panel set up by U.N. Secretary-General Ban Ki-moon found the army committed large-scale abuses and that as many as 40,000 civilians were killed in the last months of the conflict. Sri Lanka says these allegations are unfounded.
But focus on the country and the rule of its president, Mahinda Rajapaksa, has increased recently with its dismissal of its independent-minded chief justice and new allegations that Tiger boy soldiers were executed after the war.
U.N. officials including Pillay, who was also a judge of the International Criminal Court, also say there is strong evidence of recent abduction and killing of domestic critics of the government, including journalists.
But in his speech to the council, Samarasinghe said boy soldiers who fought for the rebels were "rehabilitated and reintegrated into society" under a policy which treated them as victims of the Tigers.
The controversy is expected to grow later this week when major campaign groups Amnesty International and Human Rights Watch show a film on the fringes of the council said to include evidence of the killing of the young son of a Tamil leader.
Sri Lanka's ambassador in Geneva has asked the council to stop the showing of the film, which he said was part of a campaign against his country based on "diabolical material," but there has been no sign that any such action will be taken. (Reported by Robert Evans; Editing by Mark Heinrich)