The government increased security at embassies Thursday after a bomb exploded at the U.S. ambassador's home, and police said they had seized dozens of weapons from right-wing extremists.

Police patrols were increased at embassies in Pretoria and consulates in other cities after a small bomb exploded Wednesday at the back gate of U.S. Ambassador William Swing's residence. No one was hurt in the blast.In other developments Thursday, police said one man was killed in black factional fighting in Natal, but the rest of the country was quiet. Some 800 people have died in recent weeks in factional battles.

South African Foreign Minister Pik Botha said the government was determined to catch whoever was responsible for the bombing at the U.S. residence.

No group took responsibility for the blast. South African press reports said it appeared to be the work of white right-wingers opposed to government plans to end apartheid and share power with the black majority.

Ambassador Swing was home when the explosion occurred, said Larry Schwartz of the U.S. Information Service. "It's a total surprise," Schwartz said. "It's never happened before."

The United States backs President F.W. de Klerk's efforts to end apartheid. De Klerk was given a warm welcome during a state visit to Washington late last month.

Right-wing whites also are angry with the United States for the limited sanctions it has imposed on South Africa to protest apartheid.

Police said in a statement Thursday that they had seized large amounts of guns, explosives and ammunition at several houses in the Pretoria and Johannesburg areas. The arms included machine guns, mines, mortars and pistols, they said.

Police commissioner Gen. Johan van der Merwe said some of the weapons were stolen by right-wingers in a raid April 14 on air force headquarters in Pretoria. He said the weapons were found after the arrest last week of fugitive right-wing leader Piet Rudolph.

Rudolph declared "war" on the de Klerk government earlier this year to try and halt efforts to end apartheid. Right-wingers were blamed for a series of bombings in Johannesburg.

White right-wing extremists claim whites and blacks cannot live together and insist whites must have a separate homeland.

Van der Merwe said some of the arms were recovered after police promised immunity to people holding them.