JOHANNESBURG, OCT. 3 -- A small home-made bomb exploded outside the Pretoria residence of U.S. Ambassador William Swing this morning, causing little damage and no injuries, U.S. Embassy and police officials said today.

No one has yet taken responsibility for the bombing, but similar incidents in Pretoria and Johannesburg over the past six months have been the work of white, right-wing extremists.

Barry Walkley, a U.S. Embassy spokesman, said a small explosive device was detonated around 1 a.m. outside the rear gate of the residence compound. "There was light damage to the gate, and the small guardhouse at the gate was damaged by flying debris," he said.

Swing, who was inside the house at the time, declined to comment on the incident but reportedly was awakened by the explosion, which could be heard throughout the fashionable Waterkloof Ridge suburb where Swing's residence is located.

A Pretoria police spokesman, Capt. Ruben Bloomberg, said it appeared that a small amount of commercial explosive had been used to make the bomb. He said the police were investigating the incident but had no indication who was behind it.

Later today, the South African government announced that it had ordered police to tighten security around all foreign missions.

Foreign Minister Roelof F. Botha issued a statement condemning the bombing. He pledged that the police would continue their investigation "until the culprits are apprehended."