"We cannot talk of foul play ... until it has been proved what has really transpired," said Tendai Biti, Tsvangirai's No. 2 in the Movement for Democratic Change party and the country's new finance minister.
He added that the crash "could have been avoided" had Tsvangirai been afforded the kind of motorcade that usually travels with President Robert Mugabe. At a news conference at party headquarters in Harare, Biti called for an investigation.
Dr. Douglas Gwatidzo, head of casualty at the Harare hospital where Tsvangirai was being treated, said the prime minister may be released from the hospital later in the day. He said Tsvangirai had head injuries and chest pains, but was in stable condition. State television showed pictures of Tsvangirai in a neck brace, which Gwatidzo said was being used to keep him comfortable.
"We might release him today or tomorrow," Gwatidzo told reporters gathered at the hospital.
Ian Makone, a secretary to the prime minister and member of his Movement for Democratic Change party, said Tsvangirai was "very devastated by the death of his wife."
Morgan Tsvangirai's brother, Casper, greeted visitors paying condolences at his brother's Harare home Saturday.
The crash occurred Friday evening on the outskirts of the capital on a decrepit road notorious for accidents. Like many in Zimbabwe, the road is in poor condition because it has not been maintained.
A U.S. Embassy official, speaking on condition of anonymity because the official spokesman was not immediately available, said Saturday that the truck involved was transporting AIDS medicine donated by the U.S. government. It was driven by a Zimbabwean contracted by the United States.
State television said the truck swerved on an uneven stretch of road. Tsvangirai's spokesman James Maridadi earlier said the Tsvangirais' car sideswiped the truck and rolled at least three times.
Police spokesman Superintendent Andrew Phiri told the state-run newspaper The Herald the truck may have struck an object on the road before it veered.
The Herald also reported Saturday that the two other people in Tsvangirai's car
- the driver and a bodyguard - were also injured. The paper added the driver and occupants of the truck were taken to a police station, but it was unclear whether they had been arrested.
Susan Tsvangirai, 50, was pronounced dead soon after arrival at a clinic about 25 miles (40 kilometers) from Harare, Makone said. He said her children were flying to Zimbabwe from Australia and South Africa and funeral arrangements were being made.
The Tsvangirais, who married in 1978 and had three daughters and three sons, often went together to political events, but Susan Tsvangirai did not have a prominent public role. Friday, they had been headed to a weekend rally in his home region, south of Harare.