Harare — Botswana has moved to quash rumours that it is bankrolling Zimbabwean opposition leader, Morgan Tsvangirai's diplomatic onslaught on President Robert Mugabe's government ahead of a crucial presidential run-off election on June 27.

This comes at a time when relations between Zimbabwe and Zambia have deteriorated over Harare's claims that its northern neighbour, which chairs the Southern African Development Community (SADC), is siding with the opposition on the political impasse.

Mr Tsvangirai was granted temporary refuge in Botswana soon after announcing that he beat Mr Mugabe in the March 29 poll, saying he feared for his life.

He was accommodated at a government guest house in the capital, Gaborone, and travelled with Botswana's new president, President Ian Khama to an extra-ordinary SADC summit in Lusaka to discuss the Zimbabwean crisis.

At the weekend, the South African media claimed that Mr Tsvangirai, who postponed his return home to launch his campaign for the run-off, was using President Khama's private jet for his diplomatic push.

But Dr Jeff Ramsay, the Botswana government's coordinator for communication and information services, dismissed the reports as false, saying the country had not assisted Mr Tsvangirai beyond offering him temporary refugee.

"Tsvangirai has not been given any plane by the president," Dr Ramsay told Mmegi newspaper. "There is no truth to that story."

Botswana is the only country that has accorded Zimbabweans fleeing political violence blamed on Mr Mugabe's supporters' refugee status.

Other countries, including influential neighbour South Africa, say there is no political strife in Zimbabwe to warrant the creation of refugee camps for the immigrants.

President Khama, who came to power last month, visited the Zimbabwean refugees at the camps last weekend and assured them that they were welcome as long as their lives were in danger in their country.

Mr Tsvangirai's Movement for Democratic Change (MDC) says 43 of its supporters have been killed in an upsurge of violence since the original polling day and 5,000 families displaced from their homes.

Meanwhile, Mr Tsvangirai reportedly wants to time his return to coincide with the deployment of SADC election observers, which is expected to begin this weekend.

Pressure is mounting on him to end his self-imposed exile to show that he cares for those facing persecution after a first round election on March 29.

United States ambassador to Zimbabwe, Mr James McGee, on Tuesday added his voice to calls for Mr Tsvangirai's return.

"There are many people in Zimbabwe who have paid the ultimate price by voting for Morgan Tsvangirai," Mr McGee said from South Africa.

"We believe that as a strong leader, he should be back showing his people that he cares every bit as much for them as they do for him."

Mr McGee was the latest in a long line of opposition sympathisers who have been urging Mr Tsvangirai to return and lead his party's campaign ahead of the presidential run-off.

In a new twist to the crisis, a leading think tank on Wednesday said there is a growing danger of a coup by military hardliners to prevent Mr Tsvangirai from toppling President Mugabe.

The International Crisis Group called for African mediation leading to a national unity government led by Tsvangirai as the best way to resolve the crisis, saying Western diplomacy would have a limited impact.

It said continued rule by Mr Mugabe, who has led the southern African country since independence from Britain in 1980, would be "catastrophic" for a nation already suffering inflation of 165,000 percent and 80 per cent unemployment.