Robert Mugabe visits Morgan Tsvangirai in hospital
Zimbabwe's Prime Minister Morgan Tsvangirai is in hospital after a car crash which killed his wife Susan.
The couple were travelling near Harare when their car collided with a truck.
An anonymous official at the US embassy in Harare told news agency AFP that the truck belonged to a US aid agency partner organisation.
In an emotional news conference, MDC general-secretary Tendai Biti paid tribute to Mrs Tsvangirai, calling her "a mother to us and to our struggle".
The Tsvangirais' vehicle rolled several times
State TV reported that the 56-year-old prime minister had suffered some injuries to his head and neck. He has been visited in hospital by President Mugabe and his wife.
The prime minister was on his way to his rural home in Buhera, where he planned to hold a weekend rally, when the crash occurred near Beatrice at about 1600 local time (1400 GMT) on Friday.
It is thought that a lorry carrying freight crossed into the lane in which Mr Tsvangirai's 4x4 was travelling and side-swiped their vehicle, causing it to roll over three times.
The AFP news agency quoted a minister in Mr Tsvangirai's Movement for Democratic Change (MDC) party as saying the driver of the lorry had been asleep at the wheel.
A local report said the driver of the truck was in police custody.
AFP later also quoted a US embassy official as saying the truck belonged to an organisation partnered with the US government aid agency USAID.
"It belongs to a partner of USAID who deliver HIV/Aids [drugs] and other medical supplies," the official said, on condition of anonymity.
The BBC's southern Africa correspondent says all Zimbabwe's roads are in a poor state of repair after years of neglect.
'Pillar of strength'
The BBC's Peter Biles, in Johannesburg, says that given the fierce rivalry between Zimbabwe's political parties, there will - inevitably - be speculation about the cause of this crash.
So far, though, MDC officials have said nothing to suggest that there may have been foul play, our correspondent says.
Morgan and Susan Tsvangirai had been married for 31 years
But in the news conference, Mr Biti said the accident could have been avoided if a police escort had been provided.
"Logic would have demanded that police escort be provided to the prime minister to warn other traffic and this tragedy could have been avoided," he said.
Correspondents say that Mr Tsvangirai was not entirely comfortable with security provided by the new government and relied on his own security teams.
Mr Biti said the MDC would carry out its own independent investigation into the accident.
Mr Biti, who broke down several times, said Mrs Tsvangirai was a "pillar of strength" to her husband and the party.
Earlier, senior MDC official Eddie Cross said her death would be "a huge blow for Morgan".
The crash came just two days after Mr Tsvangirai delivered his maiden speech to parliament after being sworn in as prime minister in Zimbabwe's power-sharing government.
He and his Susan, 50, who married in 1978, had six children.
A look at the important role Susan Tsvangirai played in her husband's life
The BBC's Andrew Harding, in Johannesburg, says that Mrs Tsvangirai was very discreet and stayed out of the limelight, but was a very important part of her husband's life.
She was a great source of strength to her husband when in the past he was charged with treason and assaulted for his opposition to Mr Mugabe, and sat through all his treason trial, our correspondent says.
She also made a point of visiting MDC members who were jailed while the party was in opposition, he adds.
Her death comes at a very challenging time for the fledgling power-sharing government, our correspondent says, and will only make matters more complicated.
The British foreign office and US state department sent their condolences to Mr Tsvangirai.
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