Morgan Tsvangirai, Zimbabwe's prime minister, has left hospital after treatment for head and neck injuries he sustained in a car crash that killed his wife.

Tsvangirai walked out of the hospital in Harare with senior party officials from his Movement for Democratic Change (MDC) on Saturday, said Haru Mutasa, Al Jazeera's southern Africa correspondent.

Mutasa said Tsvangirai was heading to the neighbouring country of Botswana for what MDC officials called a "proper medical check up" following Friday's crash.  She said the prime minister could be back in Zimbabwe as early as Monday.

"The fact that he did not address hundreds of supporters outside the hospital [on Saturday] is fueling speculation" about the cause of the crash and the circumstances surrounding it, Mutasa said.

The crash occurred three weeks after Tsvangirai was sworn in as head of a national unity government following a disputed elections between the MDC and President Robert Mugabe's Zanu-PF party.

'MDC investigation'

But senior officials in the MDC have not said that they suspect foul play to be a cause of the crash, she said.

"We cannot talk of foul play ... until it has been proved what has really transpired," said Tendai Biti, secretary general for the MDC and the country's finance minister.

Biti called for a police investigation into the crash during a news conference at MDC headquarters on Saturday and said the party will conduct its own investigation.

"If there had been a police escort, what happened would not have happened," Biti said. "The authorities could have avoided this omission."

Truck hit car

Tsvangirai had been travelling to a rally south of Harare, the capital, when his car was hit by a lorry travelling in the opposite direction, an MDC minister told the AFP news agency.

MDC officials comforted one another after an official confirmation of the crash  [AFP]

Susan Tsvangirai was killed instantly while her husband suffered some head and neck injuries, state television said.

Mutasa, Al Jazeera's correspondent, said that Tsvangirai's car was travelling as part of a convoy at the time of the crash.

"People are wondering how this could happen if he were travelling in a convoy. Why was his car the only one apparently damaged?" she said.

"The coalition government is very fragile and people will speculate and start reading into it; they know the relationship between Tsvangirai and Mugabe was never that good to begin with."

Fragile government

"MDC officials are being very careful and don't want to cause any unnecessary tension in Zimbabwe," Mutasa said. 

"They do not want to make the [three-week-old] fragile coalition government any weaker than it already is." 

While Tsvangirai's wife was not actively involved in the MDC, she has accompanied her husband at the party's campaign rallies over the past 10 years.

They had been married for 31 years and have six children.

Tsvangirai was sworn in as prime minister of a national unity government in February after months of political wrangling between Zanu-PF and the MDC over a disputed presidential election, which the MDC claims Tsvangirai won.

The new adminstration is tasked with tackling severe food and fuel shortages, record hyperinflation and a cholera outbreak that the World Health Organisation (WHO) says has killed at least 4,000 people.

Mugabe, a long-time rival of Tsvangirai, visited him in hospital with his wife on Friday but did not speak to reporters.