The demonstration was arranged by the Infected Children's League, and among the protesters on Tuesday were about 100 relatives of children suffering from the virus who gathered outside the United Nations headquarters in Tripoli as anti-riot police and ambulances stood by.

The protesters, most of whom were students, chanted: "We want to get our children's rights" and "Bush supports criminal nurses".

Some raised banners calling for the death sentence to be carried out against the nurses.

On Monday, Bush told reporters after meeting Bulgarian President Georgi Parvanov that the US government believed the nurses should be freed.

Experiment

Five Bulgarians and a Palestinian 
were sentenced in May 2004

In May 2004, a Libyan court sentenced five Bulgarian nurses and a Palestinian to death on charges they infected Libyan children with HIV-contaminated blood in an experiment to find a cure for Aids.

The defendants have appealed their verdicts while international observers said the charges were contrived and confessions extracted by torture.

Tuesday's protesters marched to a hotel where several US diplomats work and delivered a letter protesting against the US defence of the detainees.

The United States is planning to establish full relations with Libya's once-outcast government by the end of the year if it is satisfied Tripoli has cleaned up its record on human rights and terrorism.