President Robert Mugabe should consider stepping down as old age and health worries catch up with the 87-year-old Zimbabwean leader, Prime Minister Morgan Tsvangirai said Wednesday.

"The question of age is catching up, the question of health is catching up. I am sure that advisably he would be in a position for the sake of the country, for the sake of his legacy, for the sake of his children to consider stepping down," Tsvangirai told a news conference.

The comments were the clearest public indication yet that Mugabe's health is failing, amid reports that the liberation leader is suffering from prostate cancer that has spread to other parts of his body.

Mugabe returned Sunday from a private visit to Singapore -- the latest in what has become an almost monthly journey.

The president, who has ruled since independence from Britain in 1980, has brushed off speculation about his health.

"As you can see, this Mugabe is fit," he told state media upon his return Sunday.

Tsvangirai declined to discuss what ailment afflicted Mugabe.

"He is not certainly suffering from malaria," Tsvangirai said, because the disease common in Zimbabwe can be treated "at the nearest hospital".

Tsvangirai also defended the expense of shuttling Mugabe to Asia for health care.

"The responsibility of the state is to look after its leaders. If the president is sick he should be attended to," Tsvangirai said.