Oct. 22 (Bloomberg) -- The U.S. urged Sri Lanka today to “more thoroughly” investigate what took place in a decisive May battle with separatist forces that trapped thousands of civilians.

The call came as the State Department released a congressionally mandated report cataloguing accounts of shelling of civilians, killings, child-army recruitment and other abuses during Sri Lanka’s offensive against the separatists this year.

The 73-page account amounts to a log of incidents carried out by the Sri Lankan government and by the Liberation Tigers of Tamil Eelam from January to May. The report doesn’t reach any conclusions on whether the incidents constituted violations of international law.

“We wanted to lay out all of these credible allegations of human rights violations,” State Department spokesman Ian Kelly said today in Washington. “The report doesn’t attempt to verify all the claims, but we believe that the claims, which are based mostly on reporting” by the U.S. Embassy, international organizations and the media, “are credible,” Kelly added.

Sri Lanka’s army defeated the last LTTE forces in a battle in May on the northeastern coast, ending the group’s 26-year fight for a separate Tamil homeland in the north and east of the South Asian island nation.

The report cited one estimate that 6,710 civilians and LTTE cadres were killed between Jan. 20 and April 20 this year and acknowledged that a significant number of additional deaths may not have been recorded.

During the reporting period, senior Sri Lankan officials repeatedly denied that the government was shelling a civilian safe zone. “However, sources alleged that the majority of shelling” in the no-fire zone was from Sri Lankan forces, the report said.

Human Shields

“Reports also indicated that the LTTE forcibly prevented the escape” of internally displaced people and “used them as human shields,” the report added.

Kelly called on Sri Lanka to open up the area where the incidents took place to international organizations so they can better investigate what happened.

“The report eliminates any reasonable doubt that serious violations of the laws of war were committed by both the LTTE rebels and Sri Lankan Government forces,” said Senator Patrick Leahy, a Vermont Democrat who wrote the requirement for the report in legislation.

“If Sri Lanka is to build real peace based on reconciliation and justice, a full and independent investigation is needed, and those responsible must be held accountable,” Leahy said in an e-mailed statement.

Rights Group

New York-based Human Rights Watch today called for an independent international investigation.

“There’s never been an official and comprehensive assessment of abuses by both sides from a government, and that gives the report much more credibility,” Tom Malinowski, Washington advocacy director for Human Rights Watch, said in a telephone interview.

Malinowski said what is needed now is an “international commission of inquiry that would more explicitly look at the question of legal liability of both sides, by both the government and the Tamil Tigers.”

To contact the reporter on this story: Janine Zacharia in Washington at jzacharia@bloomberg.net.

Last Updated: October 22, 2009 17:15 EDT