Abuja - Nigerian President Muhammadu Buhari is "hale and hearty", his government said on Thursday, denying rumours in the press and on social media that he was seriously ill or even dead.Last week, the 74-year-old went to London for "routine medical check-ups" - the second such trip this year, the presidency said.But rumours that his health was failing began to circulate following reports that officials were planning to send a delegation to Britain to assess his condition.The reports were swiftly denied by Information and Culture Minister Lai Mohammed, who said they contained "no iota of truth" and that there was "no plan to send any emissary to London" to see him. "The president is hale and hearty in London," he insisted.Over the weekend, Buhari's spokesperson Garba Shehu also denied reports he was unwell, some of which even suggested he had died. "He is alive and well! President Buhari is not magical. He cannot be holidaying in the UK and be in Germany, dead or alive, at the same time," he said. A day later, Buhari posted a picture of himself on Twitter relaxing with his feet up on a table, watching a Nigerian news channel on television. Wealthier Nigerians frequently travel overseas for medical treatment because of the poor state of healthcare in the West African nation.But his visit to London sparked anger, with Nigeria's medical association saying it contradicted Buhari's pledge to end medical tourism.The health of the head of state has long been a sensitive issue. President Umaru Yar'Adua died in 2010 from a long-standing, but undisclosed, kidney condition.And there was also controversy over the 1998 death of military ruler Sani Abacha, who officially died of a heart attack, but rumours persist that he met a more lurid end.