Updated

Zimbabwe's prime minister said Monday that a car crash that killed his wife was an accident and that there was "no foul play" in the collision, despite at least three previous assassination attempts against him.

Wearing dark glasses over a swollen eye after undergoing treatment for his injuries, Morgan Tsvangirai told supporters he would overcome the loss of his wife, Susan, and continue moving ahead with Zimbabwe's unity government.

Zimbabwe's long history of political violence blamed on President Robert Mugabe's forces fueled speculation that the Friday crash was not accidental. A number of Mugabe's opponents have been killed in suspicious car accidents.

But Tsvangirai said: "In this case I want to say there is no foul play. It was an accident that unfortunately took away her life."

Tsvangirai returned to Zimbabwe's capital Monday after receiving medical treatment in neighboring Botswana.

The couple's Toyota Land Cruiser collided with a truck carrying U.S. aid on the outskirts of the capital on a notoriously dangerous road.

State television said the truck swerved on an uneven stretch of the road that is poorly maintained, like many in Zimbabwe. Tsvangirai's spokesman said the car sideswiped the truck and rolled at least three times.

A rally in honor of Susan Tsvangirai will be held Tuesday on the prime minister's 57th birthday. The funeral will take place on Wednesday.

Tsvangirai said he and his wife of 31 years had gone through "trials and tribulations together." He said he returned to resume his duties because that is what his wife would have wanted.

"It is painful for us, but we have to look forward ... because she would have wanted us to continue moving on," he said.

Thousands of mourners were keeping vigil outside the house where Susan Tsvangirai's body is to lie in state.

The U.S. ambassador to Zimbabwe, James McGee, was among the many dignitaries who came to pay their condolences.

"I am very sorry for Tsvangirai and his family," McGee said. "I hope that he can get through this, be strong and go forward."

The death of Tsvangirai's wife has triggered an outpouring of grief across the country in a show of the couple's popularity.

This is in comparison with the open dislike for Mugabe's wife, Grace, who recently punched a British photographer in the face with her diamond-encrusted rings while in Hong Kong.

"I am saddened by the death of Susan," said Mike Garikai, one mourner gathered outside Tsvangirai's house. "Tsvangirai must remain steadfast."

Tsvangirai traveled to Botswana on Saturday after spending one night in a Zimbabwean hospital following the crash.

Last year he spent months in Botswana, fearing for his life at the height of a standoff with Mugabe — the man with whom he formed a joint government in February.

Tsvangirai's party has called for an investigation into Friday's crash and has questioned the security measures for the prime minister.

Zimbabwe's coalition was formed after a dispute over the presidential election nearly a year ago and months of state-sponsored violence against members of Tsvangirai's Movement for Democratic Change and independent political activists.

But the start of the new government has been troubled, and support for Tsvangirai has been falling amid doubts over how much power Mugabe is prepared to relinquish. After the accident Friday, Mugabe and his wife went to the hospital to see Tsvangirai.

There also were fears that his wife's death would break his spirit, but it seems he is finding solace in the nation's sympathy.

Max Chimusoro, who came from a province northeast of Harare to pay his respects, said the accident could not have happened at a more critical stage in Tsvangirai's life.

"We urge him to soldier on and fulfill the dreams he began with Susan. He must not look back," he said.

Zimbabwe's unity government faces the world's highest official inflation rate, a hunger crisis that has left most of its people dependent on foreign handouts and a cholera epidemic blamed on the collapse of a once-enviable health and sanitation system.

The United Nations said Monday that the number of cholera deaths had topped 4,000, with more than 89,000 cases.

In neighboring South Africa, the waterborne disease has killed 59 people and infected 12,324 since it spread from Zimbabwe in November, the country's health minister said.