By Nelson Banya

HARARE (Reuters) - President Robert Mugabe returned home on Thursday, looking fit, after a trip to Singapore that had ignited speculation the veteran Zimbabwean leader was seriously ill.

The 88-year-old President, who has ruled the southern African country for more than three decades, landed at Harare's main airport in a white chartered plane accompanied by his wife Grace.

A Reuters reporter saw Mugabe joking and laughing with Vice President Joice Mujuru, often touted as his possible successor.

Webster Shamu, the information and publicity minister, blamed western media for spreading false reports about Mugabe's health.

"As you can see, he is fit as a fiddle. Why do we spread rumors? It's all lies told by a press driving an imperialist agenda," he said to a group of reporters at the airport.

Media had speculated that Mugabe had gone to seek vital medical attention in Singapore, where he travelled eight times last year for medical check-ups.

Mugabe did not speak to waiting reporters but is expected to chair a weekly cabinet meeting later on Thursday. The cabinet meeting venue is closed to the media.

Mugabe shares power with political rival Prime Minister Morgan Tsvangirai in a fragile coalition formed three years ago.

The former guerrilla leader has been the subject of several health scares in recent years, with some reports saying he has prostate cancer, but in February interviews with state media he laughed off suggestions that he was seriously ill.

Mugabe and close aides have kept his health a closely guarded secret.

Some members of his ZANU-PF party are afraid that, should Mugabe die in office without settling a bitter succession battle, the party could erupt in internal conflict and destabilize the country.

Although ZANU-PF officials rally behind Mugabe in public, in private many want him to retire and pass the baton to a younger person as they fear his advanced age may cost the party victory in an upcoming election.

But while some ZANU-PF members see Mugabe as a political liability, they recognize him as the only person able to control the highly partisan Zimbabwean army led by veterans of the 1970s independence war.

Many are also unsure whether his potential successors can defeat ZANU-PF's most formidable opponent, Tsvangirai, in a free election. Elections must be held by next year under the terms of their power-sharing deal.

(Reporting by Nelson Banya; Editing by Robin Pomeroy)