Nigeria's government said on Tuesday there was a case of Ebola in the capital, Abuja, after laboratory tests confirmed the viral infection.
Health Minister Muhammad Ali Pate told the public broadcaster that the female patient had travelled from Uganda in East Africa.
"She is in isolation, and she is receiving quality medical care. Contact tracing has been conducted, and it's under way as we speak, with 44 contacts already identified," Pate told public broadcaster NTA.
Asked for comment, Ugandan government spokesperson Alan Kasujja said: "There's no Ebola in Uganda."
Pate said in a statement that the patient had been admitted to a private hospital in Abuja, where she had received care for several days before the diagnosis was confirmed.
"Nigeria successfully contained Ebola in 2014, and we have the experience and public health systems to respond to this case," the minister said in the statement.
An Ebola outbreak was declared in Democratic Republic of Congo in mid-May and has since grown into the world's second-largest outbreak ever, caused by the rare Bundibugyo strain.
Uganda reported 20 cases in May and June, mostly imported from Congo, but was declared free of the virus by the World Health Organization in August.
Kenya has reported nine Ebola cases this month, all linked to a person who had travelled from Congo.
Africa's top public health agency has started mobilising support for Nigeria, said its head, Jean Kaseya.
"This Bundibugyo Ebola outbreak has already become the most geographically extensive in history, affecting ... countries spread across three regions of Africa," Kaseya said in a post on X.