Morgan Tsvangirai, Zimbabwe's prime minister, has described the car crash that injured him and killed his wife as an accident, dampening speculation that it had been an assassination bid.

Tsvangirai made his comments to mourners at his home in Harare on Monday, after returning to Zimbabwe from Botswana where he had been receiving treatment for his injuries.

"When something happens, there is always speculation but I want to say in this case, if there was any foul play, it was one in a thousand," Tsvangirai said.

"It was an accident and unfortunately it took her life."

Tsvangirai's wife Susan was killed on Friday when a foreign aid lorry collided with their car and flipped it over as the two were travelling to a rally south of Harare.

'Genuine accident'

Political tensions with Robert Mugabe, Zimbabwe's president and an unhappy partner with Tsvangirai in the country's new unity government, had prompted speculation over the cause of the crash.

Following the accident, Tsvangirai flew to Botswana for treatment, fuelling speculation that he feared for his life.

Tsvangirai's party, the Movement for Democratic Change, said security had been lax and vowed to conduct its own investigation into the crash, but warned against speculation that it had been an assassination attempt.

Soon after the crash, Britain said the lorry involved was operating as part of a joint US-UK aid venture and that "all indications are that this was a genuine accident".

Tsvangirai returned to Harare on Monday, where he was meet by government officials at the airport but did not speak to reporters.

He did not have any visible  bandages, although his face and head appeared swollen.

A public memorial for Susan Tsvangirai is planned for Tuesday, followed by a burial ceremony on Wednesday in the town of Buhera.