COPENHAGEN, July 15, 2008 (AFP) - A Copenhagen judge on Tuesday ruled that a custody order issued for two Tunisians suspected of plotting to kill a Danish cartoonist who satirised the Prophet Mohammed was legal, judicial sources said.

The two men, aged 26 and 36 and residents of Denmark, have been held in custody at the Danish intelligence agency PET's request since February 12, when they were arrested on suspicion of planning to murder Kurt Westergaard.

Westergaard is one of 12 cartoonists whose drawings were published in a Danish newspaper in September 2005.

PET has argued that the pair present a threat to national security and has demanded that they be held in prison pending a government ruling on whether to expel them to their native Tunisia without trial.

The two have not been charged with a crime. PET has not wanted to prosecute the pair because it does not want to be forced to disclose its sources and methods.

Two lower courts had previously ordered the men held until their expulsion, but their lawyers brought the case to Denmark's Supreme Court, charging their treatment was a violation of international human rights conventions.

The Supreme Court earlier this month demanded a new judicial examination of the arrest of the two suspects, and as a result the case was back in the Copenhagen district court on Monday and Tuesday.

'Their placement in custody is legal,' judge Marianne Madsen said in a statement.

She said that information provided by Danish police and PET showed it was 'likely that that the two Tunisians were in the process of preparing a terrorist attack against one of the Mohammed cartoonists.'

The court also ruled that the pair presented a threat to Denmark's national security.

Lawyers for the two men said they would appeal Tuesday's ruling.