COLOMBO, Sri Lanka - The UN's political chief will press Sri Lanka's government to speed up the release of nearly 300,000 ethnic Tamil civilians detained since the end of the country's civil war in displacement camps during a visit starting Wednesday, the United Nations said.

International rights groups have said holding the civilians is an illegal form of collective punishment and urged the government to let them live with relatives, friends or host families in the area. Aid workers fear conditions will become dire in the camps when monsoon rains start next month.

The government says it cannot release the civilians until it finishes screening them for potential rebel fighters left over from the 25-year civil war that ended in May, and until land mines are cleared from their villages in the north.

UN Undersecretary-General for Political Affairs B. Lynn Pascoe plans to visit the refugee camps to "obtain a firsthand view of the situation of internally displaced persons," the UN office in Colombo said in a statement.

Pascoe will also meet President Mahinda Rajapaksa and will focus discussions with him and other government officials on "the resettlement of internally displaced persons, political reconciliation and the establishment of a mechanism of accountability for alleged human rights violations in the context of the conflict," the UN said.

He will also hold talks with political and civil society leaders during his three-day visit, it said.

Pascoe said Monday that the UN was "particularly concerned" about the nearly 300,000 Tamils detained in the military-run camps and wants them out and home "as soon as possible."

Last Friday, Sri Lankan authorities freed nearly 10,000 people from the overcrowded camps, where their movements are restricted and sanitation is poor. The government said it previously resettled more than 5,000 people and aims to return 80 per cent of the displaced Tamils to their homes by the end of the year.

Tamil rebels fought for a separate state for more than 25 years, claiming decades of discrimination by the Sinhalese majority. The UN says between 80,000 and 100,000 people were killed during the war.