JOHANNESBURG, South Africa (AP) _ Police launched a manhunt Thursday for black gunmen who killed four people, including three whites.

Witnesses said three gunmen opened fire with AK-47 assault rifles outside a scrap metal shop early Thursday morning, killing some people in their cars.

Authorities offered a $16,000 reward for help in capturing the assailants, who fled into a nearby squatter camp.

Maj. Eugene Opperman said a motive had not yet been established.

The attack was similar to previous shootings of whites by blacks linked to the Azanian People's Liberation Army, the military wing of the small, militant Pan Africanist Congress.

Police said two white men, a white woman and a black man were killed. A black man and woman and a white man were injured.

APLA has claimed responsibility for a series of attacks on police and white civilians that are believed to have killed dozens of people.

The PAC calls the attacks part of an armed struggle against apartheid. It joined political negotiations on ending white rule this year and has come under pressure to cease armed struggle.

Earlier this week, a PAC spokesman said the group agreed ''in principle'' to end armed struggle, but needed further discussions with the government.