Three people have been injured by a bomb outside a courthouse in Cape Town.

The explosion happened on a day when two members of the vigilante group People Against Gangsterism and Drugs (Pagad) were to appear on charges of possessing a pipe bomb and hand grenade.

An emergency medical services doctor at the scene said two of the injured passers-by had suffered cuts and bruises, but refused treatment.

A third was taken to the hospital with facial burns, he said.

Police said a bomb had been placed in a motorcycle outside the main entrance to the court building in the suburb of Wynberg.

The explosion occured shortly before the courts closed for the day, and police said that the incident could have been far worse if the explosion had occured as all the staff were leaving the building.

Police have blamed Pagad for a wave of bombings that have targeted police, restaurants, clubs and other businesses.

Pagad has consistently denied planting bombs.

The group says it is the victim of an elaborate plot by members of the security forces to smear its name and undermine its role as a force of law and order in the violent Cape Flats townships.

Set-back for police

Southern Africa correspondent Greg Barrow says the relatively small explosion, will have larger ramifications for the South African police, who believed they were on the brink of a breakthrough in their long-running investigation into a spate of bomb attacks in the city.

The difficulties faced by the police in controlling gangsterism and terror have prompted the Safety and Security Minister, Steve Tshwete, to consider imposing tougher laws designed to increase police powers of arrest and interrogation.

Some human rights groups have warned that such move is a step back to the bad days of apartheid policing.