Fourteen people were injured when a mine exploded today outside the downtown Johannesburg offices of an Army medical unit. A police spokesman said none of the injuries was serious.

The explosion, which wrecked part of a bank building where the offices were situated, indicated a possible revival of insurgent actions after a lull of nearly nine months.

The ninth anniversary of the Soweto uprising occurs June 16 and is traditionally a time of black militancy. Yesterday, an insurgent shot dead a black policeman who challenged him in the tribal "homeland" of Bophuthatswana, northwest of Pretoria. Police in the territory said today they were still trying to track down the insurgent.

There was a spate of mine explosions in Johannesburg and the port city of Durban last August, timed to coincide with elections by the mixed-race and Asian minorities that were held under a new constitution. Black nationalists have denounced it as tokenism.

Several agents of the underground African National Congress were arrested after these attacks, which were aimed at military and other administration targets. While the insurgent activities tailed off after the arrests, there was a surge of internal unrest that continues. Nearly 400 people have been killed, 1,500 injured and 10,000 arrested.