JAFFNA, Sri Lanka -- Sri Lanka's ethnic Tamil leaders on Sunday asked the top UN human rights official to help determine the fate of more than 4,000 civilians reported missing in the country's long civil war amid the government's assertion that most of them are probably dead.

The UN official, Zeid Raad al-Hussein, met with the chief minister of Sri Lanka's Northern Province, the centre of the civil war, which ended in 2009. Zeid is on a four-day visit to Sri Lanka to review measures taken by the government to investigate alleged war abuses during the war.

Both the Sri Lankan government and the defeated Tamil Tiger rebels are accused of serious human rights violations. According to UN estimates, up to 100,000 people were killed in the 26-year war, but many more are feared to have died, including up to 40,000 civilians in the final months of the fighting.

The UN Human Rights Council last year adopted a consensus resolution in which Sri Lanka agreed to an investigation with foreign participation.

Zeid said he discussed several issues with Northern Province Chief Minister C.V. Wigneswaran and other provincial officials, including the missing people, detentions without trial and military-occupied private land. He said he would take the issues up with the central government.

"The discussions very much focused on the challenges faced by the province, but also the plans and achievements in that regard, and the people who aspire to see more information in terms of those detained and those missing and the issue of release of lands," Zeid said.

He said the discussions would continue during his visit.

Wigneswaran said he gave Zeid a list of the more than 4,000 people reported missing, with dates and places where they were seen last.

Many civilians have not been heard from since they were picked up by police or military personnel at their homes or abducted by pro-government militia during the war. Relatives say there are many whom they personally handed over to the military at the end of the fighting, after the military requested the surrender of anyone who had even the smallest link to the now-defeated Tamil Tiger rebels, promising their early release.

Sri Lankan Prime Minister Ranil Wickremesinghe, who was elected last year, has said most of those reported missing are probably dead. He said that the new government found no secret detention centres being run by the state, as suspected by families of the missing, and that there are only 292 people in government detention.

Wigneswaran said Zeid opposed the suggestion of negotiating an amnesty for Tamil rebel suspects detained for years without trial. Zeid said releasing innocents through a quick and proper legal process would be the best course of action.

Since defeating his nationalist predecessor last year, Sri Lankan President Maithripala Sirisena has released some land and promised speedy trials for detainees. But Tamils have complained that the authorities are slow in fulfilling their promises.