About 15,000 African National Congress supporters marched through downtown Johannesburg and Pretoria Thursday, demanding the country's white rulers resign in favor of a multiracial interim government.

The demonstrators - singing, dancing and waving ANC flags through the streets - also called on the government to end black factional violence, which has claimed almost 1,000 lives since August."If this violence does not end, it will put the peace process in jeopardy," Winnie Mandela, wife of ANC leader Nelson Mandela, told a cheering crowd of 5,000 in Pretoria.

Mac Maharaj, an ANC leader, told about 10,000 supporters in Johannesburg: "We say to the government: `Stop stalling on negotiations' . . . we want an interim government now."

The marchers in both cities called on the government to speed up black-white negotiations on ending apartheid and to make good on its promises to release all political prisoners and allow the return of exiles.

President F.W. de Klerk has pledged to end apartheid and negotiate a new constitution that will allow blacks and whites to share power.

But the president has rejected demands of an interim government while negotiations take place.