Abuja - Nigerian President Muhammadu Buhari returned to the country on Friday after a medical leave of a month and a half that raised questions about his health and some calls for his replacement, but he made clear that whatever was ailing him was not yet over.Buhari told reporters that Vice President Yemi Osinbajo would remain in charge of Africa's most populous nation over the weekend as he rested, and he revealed the first details of his health condition, including blood transfusions. He hadn't been so sick in decades, he said.Photos of his arrival in the capital, Abuja, showed the lanky president smiling and walking without assistance. "I feel much better now," Buhari said. "I have rested as much as humanly possible."He said he would have "follow-up" in the coming weeks. Sahara Reporters, a New York-based Nigerian news agency, reported that Buhari indicated he would return to London for more treatments.Few details had been released about Buhari's medical leave in London. When he left Nigeria on January 19, the government said it was for routine medical checkups and that he would return in early February.Instead, the 74-year-old remained out of sight for weeks while anxiety rose in Nigeria, which is grappling with crises including Boko Haram extremist attacks and an economy that last year contracted for the first time in a quarter-century.Some expressed anger at taxpayer-funded treatment for top officials overseas while people at home cope with poorly funded health care. "I have received, I think, the best of treatment I could receive," Buhari said on Friday. Others in Nigeria suggested that Osinbajo, a 59-year-old lawyer and pastor who handled matters in Buhari's absence, should stay on and lead the country, one of Africa's largest economies and top oil producersA statement on Thursday from special adviser Femi Adesina said Buhari's "holiday" had been extended on doctors' recommendations for further testing and rest. It gave no details about the health of the president.The statement also said Buhari expressed appreciation for Nigerians who have "prayed fervently" for him during his absence.Adesina said on Friday that Buhari and Osinbajo would "continue to do the job together," and he criticised some in Nigeria for causing "mischief" during the president's absence.The adviser said Buhari on Monday would send a letter to the National Assembly making his return to work "formal and constitutional."During his long absence, Buhari spoke once by phone with President Donald Trump as the new US leader reached out to a couple of Africa's largest economies.