Zimbabwe's prime minister, injured in a car crash that killed his wife, has left his troubled homeland for medical treatment in Botswana, an official that neighboring country said Sunday.

Clifford Maribe, spokesman for Botswana's foreign ministry, said Morgan Tsvangirai arrived in Botswana Saturday, a day after the crash. State media in Zimbabwe had said only that Tsvangirai had left the country for treatment, and his party had refused publicly to specify where he had gone.

A party official, though, had said on condition of anonymity that the prime minister was in Botswana, where Tsvangirai spent months last year, fearing for his life in his homeland at the height of a standoff with President Robert Mugabe.

Last month, Tsvangirai and Mugabe formed a coalition government, but the union has been rocky from the start.

Botswana President Seretse Ian Khama has been one of the few African leaders to openly criticize Zimbabwean Mugabe, who has ruled Zimbabwe since independence from Britain in 1980 and is accused of destroying its economy and trampling on democratic and human rights.

Last year, Mugabe's government accused opposition militants of training in Botswana to try to overthrow Mugabe, and several activists face charges in the alleged plot. The MDC and Botswana denied the allegations, and South Africa and other governments in the region have dismissed them as baseless.

Zimbabwe's long history of political violence blamed on Mugabe's forces -- including several assassination attempts on Tsvangirai -- is now fueling speculation Friday's car crash was not an accident. Tsvangirai's departure for Botswana will raise new questions about his and his country's future, particularly as no return date has been set.

The government-run Sunday Mail quoted Nelson Chamisa, a spokesman for the prime minister's Movement for Democratic Change party, as saying Tsvangirai left after consultations with his family, party and government "for further medical examination and attention just to make sure that we have exercised due diligence. We are not leaving any medical stone unturned."

Chamisa would not say when Tsvangirai would return, telling the Mail that "is going to be a function of the progress that is going to be made in the examination."

Tsvangirai's party called Saturday for an investigation into the crash, and said it could have been avoided had Tsvangirai had the kind of motorcade that travels with Mugabe. Since becoming prime minister, Tsvangirai usually travels in a convoy of four or five cars with his own and government guards, while Mugabe travels with dozens of cars and motorcycles.

The coalition was formed after a dispute over presidential elections nearly a year ago and months of state-sponsored violence against MDC members and independent political activists.

Tsvangirai was headed to a weekend rally in his home region when his four-wheel-drive vehicle collided with a truck carrying U.S. aid on the outskirts of the capital on a notoriously dangerous road. State television said the truck swerved on an uneven stretch of the road, which, like many in Zimbabwe, is poorly maintained. Tsvangirai's spokesman said the car carrying the prime minister, his wife, a driver and a bodyguard sideswiped the truck and rolled at least three times.

Susan Tsvangirai, 50, was killed. The driver and the bodyguard were injured, but not seriously. Dr. Douglas Gwatidzo, head of casualty at the Harare hospital where Tsvangirai was treated, said the prime minister had head injuries and chest pains.

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.

Tsvangirai, who turns 57 Tuesday, formed the MDC a decade ago. As it emerged as a serious political challenger, Tsvangirai repeatedly faced the wrath of Mugabe's ZANU-PF party. He has been beaten and was once nearly thrown from a 10th floor window by suspected government thugs.

Zimbabwe has the world's highest official inflation rate, a hunger crisis that has left most of its people dependent on foreign handouts and a cholera epidemic blamed on the collapse of a once-enviable health and sanitation system.