Secretary of State Colin Powell told a student audience Friday that the United States would be "with you every step of the way into the future" but would not attempt to make peace among Africans.
At the same time, Powell issued a sharp denunciation of Robert Mugabe, president of neighboring Zimbabwe, suggesting that he should allow democratic elections in that nation roiled by turmoil.

While other countries have welcomed democratic changes, Powell said, Mugabe "seems determined to remain in power."

In a speech that drew loud but isolated heckling, Powell said the Bush administration would continue its role of active economic help and political aid to Africa but has no intention of getting involved militarily in internal disputes on the continent.

Several dozen protesters shouting such slogans as "Powell go home" and "free Palestine," blocked Powell's motorcade from leaving the University of the Witwatersrand for a half hour after his speech.

When his motorcade finally barreled through the line of demonstrators, several protesters banged on the hood and roof of his limousine. A uniformed South African policeman and a plainclothes U.S. diplomatic security agent were hurt in the scuffle and fell to the ground. They were immediately helped up.

In his speech, Powell, the first black secretary of state, pledged the Bush administration's active support.

"Africa matters to America -- by history and by choice," he said to applause.

Earlier, Powell toured an AIDS clinic in nearby Soweto. He said he is convinced that South African President Thabo Mbeki is committed to combatting AIDS. Mbeki earlier had caused controversy by questioning the link between HIV and the disease.

Powell, who has made the global battle against AIDS a primary theme of his four-nation Africa trip, met with South African Foreign Minister Nkosazana Diamini-Zuma in Pretoria. Both said U.S.-South African relations are in good shape.

Zuma defended South Africa's role in combatting AIDS, saying those who criticize her nation are "missing the point."

"We are concerned about the welfare of our people," she said, adding "Major attention should still go to education."

Powell agreed. "Prevention is perhaps the key to it all," he said.

After arriving in South Africa Thursday evening from the West African nation of Mali, Powell met with Mbeki in the Union Building, which houses the president's offices, for about 45 minutes.

The two leaders said they discussed various African problems, including strife in neighboring Zimbabwe and in Congo, and also discussed the peace process in the Middle East.

Powell said President Bush shared his enthusiasm for African issues.

"He is very, very interested in what my report will be when I get back," Powell said.

For his part, Mbeki told reporters he was certain that Bush would remain as engaged in Africa as the former Democratic Clinton administration, "I know that for a fact." Mbeki said he was coming to Washington at Bush's invitation next month.

Powell was asked if he had raised the issue of AIDS with Mbeki. South Africa leads the world in the number of people infected with HIV, the virus that causes AIDS.

"I didn't have to discuss that. The president is fully seized with the problem, doing everything possible," Powell said.

Mbeki two years ago suffered withering international condemnation for entertaining the views of fringe theorists who doubt the link between HIV and AIDS. Mbeki has moderated his position somewhat since then.

Earlier, Bush's foreign-aid chief, Andrew Natsios, said that Mbeki had "unorthodox views on this issue."

Natsios, who has been traveling with Powell, said African leaders need to do more to speak out on the causes and prevention of AIDS. He suggested South Africa got a late start in recognizing the depths of its own AIDS problem.

One in five of the adult population is now infected, and this number could soon rise to one in four, said Natsios, head of the U.S. Agency for International Development.

"There's an aversion by some leaders in some countries to talk about this," Natsios told reporters aboard Powell's plane.

Powell next travels to Kenya and Uganda.