A federal judge in New York is to hear a plea for the release of an American citizen accused of plotting a "dirty bomb" attack in the US.

The suspect's lawyer has challenged the arrest, questioning the legal basis for classifying Abdullah al-Muhajir as an enemy combatant - a term which allows for his indefinite detention without trial.

Our interest is in finding out what he knows

Defence Secretary Donald Rumsfeld

Mr al-Muhajir - who has been linked to al-Qaeda by US officials - was arrested on 8 May at Chicago's O'Hare international airport, but his detention was only announced by the government on Monday.

His lawyer, Donna Newman, said there were no charges against her client and added that the legal community was outraged at his being detained "without time limit, or the right to counsel".

Mr al-Muhajir has been transferred to military custody and it is unclear whether the Manhattan federal court has jurisdiction in this case.

President George W Bush said on Tuesday that there was a "full-scale manhunt on" for anyone else believed to be involved in an alleged al-Qaeda plot to detonate a radioactive bomb in the US.

Military detention

Mr Bush said Mr al-Muhajir, born Jose Padilla, had links to the al-Qaeda terror group, which the US blames for the 11 September attacks in New York and Washington.

Al-Muhajir was arrested on his return from Pakistan

"This guy, Padilla, is a bad guy. And he is where he needs to be detained," Mr Bush said.

Mr Bush said that US authorities are now hunting down any terror associates Mr al-Muhajir may have.

"As we run down these killers or would-be killers, we'll let you know," he said.

Mr al-Muhajir, a US citizen of Puerto Rican descent, has been handed over to the army and is being detained at a military facility in South Carolina.

Ms Newman said she had not been allowed to speak to him since his transfer.

Legal quagmire

US Defence Secretary Donald Rumsfeld said his government was "not interested in trying him at the moment".

How does a dirty bomb work?

A conventional bomb is packed with radioactive isotopes The force of the explosion spreads radioactive material over a wide area Likely to cause radiation sickness in any exposed to the contaminated area Massive disruption ensues Read more about dirty bombs

"We're not interested in punishing him... we're interested in finding out what in the world he knows," Mr Rumsfeld said.

Civil rights groups have accused the US of changing Mr al-Muhajir's status simply in order to detain him indefinitely without bringing a charge.

The suspect is alleged to have been planning to build and explode the bomb, which can spread material highly toxic to humans.

Investigators are said to have known about Mr al-Muhajir for some time.

Officials said he was stopped in the "initial planning stages" and no specific targets had been selected.