The UN refugee agency yesterday urged Malaysian authorities to free 13 people from Indonesia and Burmese detained in a crackdown on illegal immigrants and denied issuing documents indiscriminately to asylum seekers.

Volker Turk, head of the UN High Commissioner for Refugees (UNHCR) in Malaysia, told AFP the 13 - 10 from tsunami-hit Aceh province and three Rohingyas from Burma were being held at the Semenyih detention centre, south of Kuala Lumpur.

"They are holders of UNHCR card. I do not know why they were arrested. They should be freed. I have informed the Home Affairs Minister (Azmi Khalid) not to deport them," he said.

Malaysia on March 1 launched a controversial operation to round up, whip and deport hundreds of thousands of illegal immigrants, mostly Indonesians, following the end of a four-month amnesty.

Home Minister Azmi on Thursday said illegal immigrants from Aceh would be spared detention on humanitarian grounds but said the UNHCR had indiscriminately issued letters to Acehnese asylum seekers.

"All these UNHCR letters cannot be accepted as bona fide . There is information that some are not genuine," he was quoted as saying by New Straits Times newspaper.

Turk however said every asylum seeker underwent a strict interview by UN officers.

"We refute the allegation. UN has a stringent process in place to ensure documents are issued to those interviewed. It is a complex process. We do not issue documents indiscriminately," he said.

Turk admitted there were "fake UNHCR documents" in circulation and said officials rounding up illegal immigrants should communicate with the agency to verify them.

Lack of workers

Meanwhile the Sunday Star newspaper said thousands of Indonesians wanting to return to Malaysia legally were stranded due to administrative delays which have hit the construction and oil palm industries which depend on cheap foreign labour.

"We acknowledge that there is a bottleneck and hope to sort things out with our counterpart (in Jakarta)," said immigration department enforcement director Ishak Mohamed.

Human Resources Minister Fong Chan Onn said the plantation sector was short of 300,000 workers and the construction sector about 200,000 workers.

The UNHCR in December had expressed fears that asylum seekers from military-ruled Burma and strife-torn Aceh would be swept up along with illegal migrants.

An estimated 400,000 illegal immigrants are still in Malaysia, many of whom sought jobs in the construction, plantation and service industries in the face of unemployment at home.

The crackdown is part of Malaysia's largest blitz to flush out illegal immigrants in three years.