A Sri Lankan government investigation into human rights abuses during its war with Tamil Tiger rebels has been disbanded with more than half of its cases unresolved, an official said Tuesday.

The decision came as the government brushed off demands for an international investigation into the final ferocious battles of the war, which ended last month after the military routed the rebels in an offensive the United Nations says killed more than 7,000 civilians.

Human rights groups accused the military of shelling civilian areas and said the rebels held hundreds of thousands of people as human shields, shooting those who attempted to flee.

A presidential commission of inquiry was established two years ago under intense international pressure to investigate earlier claims of abuses in the war. It was assigned 16 cases of alleged abuses by both sides, including the 2006 execution-style slaying of 17 aid workers for the French organization Action Against Hunger.

Nissanka Udalagama, a former Supreme Court justice who chaired the commission, said it had only completed work on seven of the assigned cases by the time its mandate expired Sunday. Extensions had been routinely granted in the past, but not this time. Instead, the commission was dissolved, he said.

"We ran out of time," he said. "If we had gotten another year, probably we could have done it."

It was not clear why the inquiry was ended.

"I have no idea what the reasoning is," said Rajiva Wijesinha, the secretary in the country's Human Rights Ministry who usually serves as a government spokesman in such matters.

Amnesty International calls for new inquiry

The commission's dissolution came days after Amnesty International accused the government of failing to seriously investigate reported abuses during the 25-year civil war. It said the few cases that are brought to trial rarely end in convictions and accused the government of using bribes, threats and even murder to eliminate witnesses.

Government officials denied the allegations.

The London-based rights group called for the establishment of an international commission to investigate allegations of recent human rights violations. The government has repeatedly rejected such calls as a violation of its sovereignty.

Udalagama said even in the cases the commission completed, it was often unable to identify the perpetrators.

In the killing of the 17 aid workers, "we are unable to pinpoint and tell exactly who it is, but there are certain possibilities," he said.

In the slaying of five young people in the eastern city of Trincomalee, he said, "What we think is that someone in uniform did it," implicating the security forces.

Investigations into some of the cases were hampered because witnesses fled abroad and the government stopped allowing the commission to take testimony via videoconferencing, he said.

Last March, an international panel of experts established to observe the commission resigned, saying the government lacked the political will to properly investigate the abuse allegations.