COLOMBO (AFP) - The Sri Lankan immigration authorities on Sunday briefly detained an Australian and a New Zealand politician on a fact-finding mission into alleged human rights abuses, officials said.

The move came days before the country hosts a Commonwealth summit, amid pressure on visiting leaders to boycott the event over alleged war crimes.

Immigration officials held Australian Senator Lee Rhiannon and New Zealand MP Jan Logie shortly before they were to hold a press conference about their mission, an opposition Sri Lankan lawmaker said.

"They were accused of breaching visa conditions, but they had 'special projects visas' to be in Sri Lanka on a fact-finding mission," Tamil lawmaker M. A. Sumanthiran told AFP.

An immigration official confirmed the pair were detained briefly at their hotel room for questioning, but declined to give details.

The Australian High Commission said the senator had been questioned about an alleged breach of her visa conditions but was later released.

"We understand that they are on their way back home according to their travel plans," a high commission official said.

Mr Sumanthiran of the Tamil National Alliance said the pair had been questioned because the government was "paranoid" about foreigners looking into the country's dismal rights record.

"Publicly, the government says anyone can come here and see for themselves, but actually they don't want the world to know what is happening here," he said.

He said the two were eventually freed because they were scheduled anyway to leave the country on Sunday.

The pair had travelled to the island's former northern war zone to look into cases of human rights abuses, four years after government forces crushed Tamil rebels to end a decades-long separatist war.

The move came less than two weeks after Sri Lanka kicked out two Australian media rights activists who were meeting local rights activists.

Canadian Prime Minister Stephen Harper has already said he will not attend the Nov 15 to Nov 17 Comonwealth Heads of Government Meeting.

Indian Prime Minister Manmohan Singh will also skip the summit over the alleged war crimes by Colombo, a government source said in New Delhi on Sunday.

Sri Lanka faced censure at the United Nations Human Rights Council over its failure to probe allegations that up to 40,000 civilians were killed by its troops in the final months of the battle with Tamil rebels in 2009, charges the country has denied.