JOHANNESBURG, South Africa — Zimbabwean President Robert Mugabe may be forced to face justice by a citizenry that has run out of patience with his regime's abuses, his main rival said in an interview Thursday.

Zimbabwean opposition leader Morgan Tsvangirai's new stance could make it even harder to dislodge Mugabe, who according to some critics is holding onto power because he fears he and his top aides will be dragged to court to face human rights abuse charges if he steps down.

Tsvangirai's hardened position on Mugabe came the same day Zimbabwean state media reported that the ruling party accused the opposition leader of plotting with former colonial ruler Britain.

The opposition leader dismissed the treason charges and said accusations that he was plotting to overthrow the Mugabe regime were "outrageous."

"We are determined to have democratic change through democratic means," not through violence, Tsvangirai told The Associated Press. "The people themselves are the ones that will change the government."

U.S. Secretary of State Condoleezza Rice said Mugabe's recent rule has been an "abomination."

"It's time for Africa to step up," she said.

South African President Thabo Mbeki has said Mugabe will not respond to a confrontational approach and has been widely criticized for saying over the weekend that Zimbabwe was not in crisis.

At a news conference, Tsvangirai called Mbeki's comments disappointing and said that it was time for him to step aside as a mediator in the crisis. Tsvangirai called instead for Zambian President Levy Mwanawasa, who has been more critical of Mugabe than Mbeki has been, to take over mediation.

Tsvangirai has said in the past that he is not interested in a "witch hunt" if he were to oust Mugabe because that would distract a new government from Zimbabwe's economic and political crises.

Nearly three weeks have passed since a presidential vote that Mugabe, accused of destroying his country's economy, is widely believe to have lost. No official results have been released, and the opposition, which says Tsvangirai won, accuses Mugabe of withholding the results to stay in power.

Human rights groups say the postelection period has seen increasing violence against Tsvangirai's supporters. Mugabe's troops also were accused of massacres in the western Matabeleland province during an armed rebellion after independence in 1980. And his brutal countrywide slum clearance operation in 2005 has been decried as a violation of human rights.

"Those who are responsible ... for gross human rights abuses" should face justice, Tsvangirai said, arguing that Mugabe would be at the head of this group.

Mugabe "is the ultimate authority. The buck stops with him," Tsvangirai said.

Tsvangirai, relaxed in a dark suit, joked during the interview that he may earn a place in record books for facing the most treason trials. In 2003, after an 18-month trial, Tsvangirai was acquitted of treason in a case stemming from an alleged a plot to assassinate Mugabe.

Tsvangirai has survived three assassination attempts, including one in 1997 by unidentified assailants trying to throw him from a 10th floor window of the trade union congress's headquarters.

Treason carries the death penalty in Zimbabwe, so Chinamasa's comments in The Herald could be seen as a new threat to Tsvangirai's life.

Tsvangirai, who has been traveling outside Zimbabwe for most of the period since the election, acknowledged in the interview that his homeland was a dangerous place for him.

"There are rogue elements there who might take the law into their own hands," he said.

But he said diplomacy, not fear, was the main reason he was not at home. He would not say when he would return, saying his priority now is mobilizing international pressure on Mugabe.

"I'll go back. It's just that I've got work to do," he said.

Tsvangirai was away from home at a time his movement was struggling. A stay-away called to force election officials to release the presidential vote count fizzled — both because few Zimbabweans can afford to miss even a day of work, and because police and militants loyal to Mugabe cracked down.

Tsvangirai said he did not participate in the decision to call the stay-away, and said it "may have been an exhausted strategy."

"I would have cautioned we must not engage in strategies that will only confirm that people are afraid," he said.

Tsvangirai's attempts to keep Zimbabwe on the international agenda were showing little result.

At the United Nations, the U.N. secretary-general and the leaders of Britain and the African Union urged Zimbabwe on Wednesday to ensure that the outcome of the presidential election reflects the will of the people and is not rigged.

But South Africa, which holds the U.N. Security Council presidency this month and organized the meeting, did not put Zimbabwe on the agenda.

At a weekend summit, the leaders of the countries neighboring Zimbabwe followed Mbeki's lead, issuing a weak declaration that did not criticize Mugabe, who did not attend.

Tsvangirai said he could not predict how long his country's political impasse would continue, and acknowledged there are limits to what the outside world can do. He said he did not know who could persuade Mugabe to step down.

"If we knew, certainly that person should be contacted immediately," he said.