By Simon Gardner

COLOMBO, Sept 21 (Reuters) - Beset by censure over a rash of civil war human rights abuses, Sri Lankan President Mahinda Rajapaksa will set out his case at the UN General Assembly next week -- but critics doubt it will wash.

Rights groups say hundreds of people have been killed or abducted since last year, when a civil war that has killed around 70,000 people since 1983 resumed after a near four-year lull. Some abuses have been blamed on state security forces.

The government says the reports are overblown and designed to tarnish its image, and has vilified United Nations envoys for voicing concerns and slammed foreign governments and rights groups for criticism.

"The government is denying what is happening on the ground," Jehan Perera of non-partisan advisory group the National Peace Council said on Friday. "All the government's denials lead to is an erosion of credibility."

Relatives of the murdered and disappeared -- some of the abuses blamed on state security forces or paramilitaries seen allied to the government, others on the Tigers -- want answers and accountability, and critics say they are getting neither.

Some government officials have said many who have disappeared have gone abroad on holiday or eloped with lovers. One even accused aid group Action Contre La Faim of being responsible through negligence for the deaths of 17 of its own local staff, whose murder Nordic truce monitors have blamed on the military.

The government has also rejected calls from rights groups and aid workers for a United Nations human rights monitoring mission, saying it would infringe on its sovereignty and that it is capable of probing abuses itself.

ABUSE PROBE FAILING

International experts observing a presidential commission probing a raft of abuses including the aid worker murders, say the commission is not cooperating fully with them, is failing to meet international standards, and is proceeding so slowly the probe is on course to fail.

"We have never been as isolated internationally as we are now," said Mangala Samaraweera, a former foreign minister who was sacked from the cabinet in February amid a political spat with Rajapaksa and is now allied to the main opposition.

"A government which obviously doesn't want to mend its ways and is determined to fight terrorism at the level of terrorists, I think they have a lot to answer for now."

The government is forging on with military offensives to evict the Tigers from territory they control, justifying its actions by pointing to how the United States is waging its own "war against terrorism".

Political and military analysts say seeking to annihilate the Tigers militarily will only result in more bloodshed, and see no clear winner on the horizon. An estimated 5,000 people have been killed since early 2006 alone, including many civilians caught in the crossfire.

Officials say the international community is being too soft on the Tigers, who have mounted repeated bombing and suicide attacks on troops and the authorities in their campaign for a separate state in the north and east.

They say abuses by the rebels, widely outlawed internationally as a terrorist group, are being overlooked.

"By and large (the criticism) is unfair, because all the factors in Sri Lanka are not being taken into consideration," an official in Rajapaksa's office said, asking not to be named. "In the rest of the world there is suppposed to be a war on terror. We are carrying out our own war on terror."

"The government is taking and has taken as many steps as possible to ensure that human rights are safeguarded," he added. "There could be shortcomings, but what is being said internationally is largely overblown."

Rajapaksa is due to address the United Nations General Assembly in New York on Tuesday.

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