JOHANNESBURG, SEPT. 28 -- Three black policemen are being held in connection with a mass killing early Saturday in which 13 black youths died and seven were injured as a result of factional rivalry in Natal Province, the police command in Pretoria said today.

The bodies of three blacks killed in other fighting between rival groups were found early today near Pietermaritzburg, police said.

Chief Mangosuthu Gatsha Buthelezi, leader of the predominantly Zulu Inkatha movement, called on the rival United Democratic Front to help resolve the Natal conflict, which has left scores dead in the past year. He and other Inkatha leaders blamed the front for the killings.

The weekend mass killing, in which Inkatha leaders said members of its Youth Brigade between 14 and 22 years of age were shot and stabbed as they tried to run from a burning house, was the worst in Natal since gunmen burst into the home of a UDF activist near Durban last Jan. 20 and killed 12 persons, seven of them children. The UDF accused Inkatha of carrying out that attack in revenge for the killing of Inkatha members.

It was not clear what role the three arrested black policemen may have played in Saturday's killings.

Joseph Mabaso, Inkatha regional chairman, said that a group of people carrying guns and spears locked the house in which the youths were sleeping and set it on fire. When the occupants tried to escape through windows, they were shot and stabbed, Mabaso said.