Tunisian police, angered at charges of killing protesters, are planning a sit-in on Tuesday outside the main government building in Tunis, security forces unions said.

"We are organising a sit-in Tuesday to put forward a number of demands and if the government continues to ignore us then we will begin an indefinite strike," Abdelkader Mathluthi, a spokesman for the federation of police unions, told AFP.

However a fellow union spokesman, Montassar El-Materi, denied that strike action was being considered "given the current security situation."

The police unions are in particular calling for a fair trial for 23 officers who have been detained on charges of killing protesters.

They were arrested in the wake of civil unrest in December and January which flared after weeks of protests initially focused on unemployment, sparked by the suicide of a young street-vendor who set himself alight on December 17 last year.

The protesting police also want to see those responsible for attacks against police stations, "the killers of police martyrs," to be brought to justice.

According to the union, 10 police officers were killed and 18 shot and injured on January 14, the day ousted president Zine El-Abidine Ben Ali was arrested as he attempted to flee the country.

Hated and feared during the Ben Ali regime, the police force feels it has been made a scapegoat for its excesses.