JOHANNESBURG, South Africa — President Mbeki ordered the army into South Africa’s townships last night as violence against black migrants spread. Mr. Mbeki has been criticized for his lack of leadership during a week of troubles, which have claimed at least 26 lives. His office said the president had approved a police request for the “involvement” of the South African Defence Force in stopping “the ongoing attacks on foreign nationals in Gauteng province.”

The finance minister, Trevor Manuel, told local radio that the troops would probably be patrolling this week. “They will be there in a back-up role,” he said. “They are there to assist the police.” Violence spread to Durban yesterday where a mob wielding clubs and broken bottles threatened a group of Nigerians. This caused some 700 black migrants to flee their homes and seek refuge in police stations and church halls.

Police in Cape Town were also put on alert amid growing fears among the area’s large population of black migrants. The xenophobic violence exploded a week ago in the Pretoria and Johannesburg areas, where it was now relatively calm.

There are an estimated 5 million foreign blacks living and working in South Africa, at least 3 million of them Zimbabweans who have fled the tyranic rule of President Mugabe in neighboring Zimbabwe.

Mr. Mbeki has announced the establishment of a “special committee” to examine the causes of the violence but his own government’s failings to address the widespread poverty within South Africa itself and deal with the deteriorating situation in Zimbabwe are blamed by opposition parties, human rights, groups and NGOs.