Zimbabwe Prime Minister Morgan Tsvangirai's party yesterday pushed for an independent probe of the car crash that killed his wife and injured him, as an official said a US aid truck was involved.

Tsvangirai, a long-time rival of President Robert Mugabe who recently became prime minister in a unity government aimed at ending months of political turmoil, remained in stable condition in hospital after the crash on Friday.

"Police are making their own investigation, we are also making our own," said Finance Minister Tendai Biti, also the number two leader of Tsvangirai's Movement for Democratic Change (MDC) party.

Biti charged that the crash could have been avoided had Tsvangirai been travelling with a police escort.

An MDC lawmaker, Eddie Cross, said "the party will insist on an independent investigation".

Tsvangirai and his wife Susan, 50, were travelling from Harare to Buhera, their rural hometown where the new prime minister was due to speak at a rally yesterday. His wife died at the scene of the crash.

Police on Friday said Tsvangirai's car collided with a truck which crossed into the oncoming lane and side-swiped the prime minister's vehicle, causing it to roll several times.

More details of the truck emerged yesterday, with a US embassy official in Harare saying it belonged to a US aid agency "partner" for Aids drug delivery.

"The truck that was involved in the crash belonged to a partner of US Aid. It's not a US government vehicle," the official said on condition of anonymity.

"It belongs to a partner of US Aid who deliver HIV/Aids and other medical supplies. The vehicle is used in a project to provide antiretroviral drugs. Whether it was carrying any aid at the time, I am not sure."

ABC News in the United States cited unnamed US officials as saying the truck belonged to a contractor working for the US and British governments.

The truck, which had a US Aid insignia on it, was purchased by US government funds and its driver was hired by a British development agency, the report said. US Aid stands for the US Agency for International Development.