There have been regular protests against the child abductions

Police dispersed demonstrators with tear gas in the capital, N'Djamena, after cars belonging to white foreigners and diplomats were attacked.

The protesters were demanding that six French aid workers charged with child kidnapping be tried in Chad.

Meanwhile, a judge in Chad rejected a request by defence lawyers seeking the release pending the trial of the six French and three Chadians still held.

If found guilty, the charity workers face several years with hard labour in a Chadian prison.

They said they believed they were rescuing Darfur war orphans, but parents of many of the 103 children almost flown to France told the BBC they were promised they would be educated locally, and never gave permission for them to leave the country.

Earlier this month, France's President Nicolas Sarkozy had said he wanted to go to Chad to bring the French aid workers from Zoe's Ark back home angering many Chadians.

Targeting French

Crowds of students began gathering in the centre of N'Djamena shortly after 0730 hours local time.

Most of the demonstrators were high school students, wearing their school uniforms and chanting anti-French slogans.

Before long, what was designed to be a peaceful protest, got out of hand, the BBC's Stephanie Hancock in the capital says.

The demonstrators began attacking white foreigners in their cars, hurling stones and shouting, "Whites - child kidnappers".

For several hours the young demonstrators took over the capital, running riot along N'Djamena's main streets and eventually converging at the French embassy.

The police used tear gas to disperse the protestors who were intent on finding French citizens to attack.

The students, who were holding banners saying "Sarkozy, out of Chad" eventually returned to the city's main square in front of the presidential palace where several thousand of them converged for a mass protest.

Riot police and soldiers are still trying to calm the situation down, although the protestors are finally beginning to wrap up their demonstration.