The Bush administration has started to encourage African states, including the continent’s most powerful democracy, South Africa, to establish a “coalition of the willing” with an eye toward pressing for regime change in Zimbabwe, State Department officials say.

While emphasizing that there is no thought being given to deploying any American troops in southern Africa in the event of an intervention and bid to topple Zimbabwe’s president, Robert Mugabe, officials told The New York Sun that Washington is keen now to persuade Zimbabwe’s neighbors to review their current “quiet diplomatic” efforts aimed at resolving the deepening crisis in Zimbabwe.

Their comments came just 24 hours after the new American ambassador to South Africa, Jendayi Frazer, told reporters in Johannesburg that there was no evidence that sanctions and quiet diplomacy were working to rid Zimbabwe of Mr. Mugabe and a regime that has been widely condemned for human rights violations and election fraud.

She said America would be willing to be part of a coalition if invited, to help return Zimbabwe to democracy, and to end Mr. Mugabe’s 24 years in power.

Ms. Frazer, a protegee of President Bush’s national security adviser, Condoleezza Rice, added: “South Africa has the most leverage probably of any other country in the sub-region and should therefore take a leadership role…There is clearly a crisis in Zimbabwe and everyone needs to state that fact. The economy is in a free fall. There is a continuing repressive environment. There needs to be a return to democracy.”

The International Parliamentary Union released a report earlier this week accusing Zimbabwe’s government of doing nothing to stop pro-Mugabe violent youth militias from attacking members of the country’s opposition party, the Movement for Democratic Change. The worsening pro-government violence is making it impossible for the opposition to operate ahead of parliamentary elections next March, say Mugabe critics.

With violence increasing, Zimbabwe’s main opposition party announced yesterday that it would not take part in future elections unless the Mugabe government implements democratic reforms. The party challenged the results of the polls in 2000 and 2002 alleging widespread fraud.

In a statement, the MDC said that it wanted a new legal framework for elections, with acceptable levels of transparency and fairness. “The MDC will not participate in elections until the political space has been opened up and a legal, institutional, and administrative framework for elections has been established,” said MDC spokesman Paul Themba-Nyathi. He says there is evidence of massive electoral fraud being planned by the government.

The more aggressive American line toward the Mugabe regime coincides with the arrival in South Africa of the British foreign secretary, Jack Straw. British officials say that the issue of Zimbabwe will top the agenda of the meetings that he will hold with members of the South African government. He is likely also to impress on the South African president, Thabo Mbeki, that he needs to take the lead in efforts to force Mr. Mugabe to go.

How responsive Mr. Mbeki will be remains to be seen, say American officials. Mr. Mbeki has favored a path of quiet diplomacy towards Zimbabwe for fear of alienating Mr. Mugabe and his Zanu-PF party. He is fearful also of catapulting Zimbabwe into an accelerated collapse that Mr. Mbeki believes could have disastrous consequences for the region and have a negative impact on South Africa, which like Zimbabwe is struggling with rising land hunger by blacks and widespread poverty.

He and his government officials have avoided criticizing Mr. Mugabe openly. That soft approach has irritated anti-Mugabe Zimbabweans and led the British government to argue that Mr. Mbeki is in effect legitimizing Mr. Mugabe with his silence. In an effort to appease critics of his “quiet diplomacy,” Mr. Mbeki backed earlier this month a new regional charter spelling out guidelines for free and fair elections issued by a group of Southern African leaders.

Mr. Mugabe has vowed to defy recent sanctions imposed on him and his government associates by Western powers and has said travel bans preventing him and 95 other government officials from visiting America or the European Union states will fail to derail his administration or persuade him to alter policy.

The hardening American line, while not including any commitment to provide military support for an outside intervention in Zimbabwe, appears similar to the approach being adopted by the Bush administration to the deepening crisis in Sudan. In that case, too, Washington is encouraging the African Union to intervene and is offering nonmilitary assistance.