Zimbabwean Vice-President John Nkomo died on Thursday after treatment for cancer in South Africa, a Zimbabwean political source said, removing a potential successor to ageing President Robert Mugabe, who has his own health problems.

Nkomo, 78, was nominated for the joint number two position alongside Joice Mujuru two years ago after a fractious meeting of the southern African nation’s ruling ZANU-PF party.

A founding member of nationalist leader Joshua Nkomo’s ZAPU before its merger with Mugabe’s ZANU-PF in the 1980s, John Nkomo was seen by many as an efficient administrator but a remote potential successor to Mugabe due to his age and ill health.

Analysts say his death will rekindle debate over 88-year-old Mugabe’s health issues and open up a succession battle as the country’s shaky coalition government edges towards a general election due this year.

In December Mugabe vowed to fight like a “wounded beast” to retain power amid grumbling within his party that he should hand over the reins to a younger leader.

He is Africa’s oldest head of state and has ruled the former British colony since independence in 1980 but has denied reports he has been receiving treatment for prostate cancer in Singapore over the last two years.

Official media were silent on Nkomo’s death but the U.S. embassy released a statement offering its condolences at the passing of “a patriot who dedicated his life to Zimbabwe’s sovereignty and prosperity”.

Mugabe and ZANU-PF are struggling to shore up support among young voters, who care more about the economy than the party’s role in leading the 1970s liberation struggle against white-minority rule.