The truck, which had a USAID insignia on it, was purchased by US government funds and its driver was hired by a British development agency, the report said.
USAID stands for the US Agency for International Development.
While on a routine delivery route, the truck apparently swerved into ongoing traffic and sideswpied the car the Tsvangirais were driving in, causing it to overturn several times, they added.
The officials said the truck has been impounded by authorities in Zimbabwe and its driver placed under arrest.
Susan Tsvangirai was killed on Friday and her husband was hurt in the accident that happened as they headed to their hometown in Buhera district.
The prime minister was taken to private hospital and is in a stable condition, Zimbabwe Finance Minister Tendai Biti told reporters after visiting him. – AFP