(CNN) Nigeria's President Muhammadu Buhari has denied claims that he died and was replaced by a clone, calling the speculation "ignorant rumors."

Buhari tweeted on Sunday that he addressed the reports while at a meeting in Poland.

"One of the questions that came up today in my meeting with Nigerians in Poland was on the issue of whether I've been cloned or not," Buhari said. "The ignorant rumors are not surprising -- when I was away on medical vacation last year a lot of people hoped I was dead."

Buhari spent long periods in London receiving medical treatment in 2017, on one occasion leaving Nigeria for more than three months.

His absence prompted intense speculation in the country about the President's health and many false reports circulated online saying he had died.

On Instagram and Facebook Sunday, the President said the belief that he had died had prompted people to reach out to Vice President Yemi Osinbajo asking to be his deputy.

"That embarrassed him a lot; we discussed it when he visited me while I was convalescing," Buhari said. "I can assure you all that this is the real me. Later this month I will celebrate my 76th birthday. And I'm still going strong!"

Presidential spokesman Garba Shehu said on Facebook that a Nigerian at a meeting in Krakow on Sunday had asked Buhari if he was real or "the much talked about 'Jubril from Sudan' -- his supposed double" -- prompting the President to affirm his identity.

Shehu said Buhari was in Poland to attend the UN Climate Change Conference, COP24.

Buhari was elected President of Nigeria, Africa's largest economy and top oil producer, in 2015.

The former general became President in his fourth attempt at leadership since he was ousted from power in 1985.

Buhari was among military strongmen who dominated Nigeria decades ago. A military coup brought him to power in 1983, and another military coup toppled him two years later.