The Nigerian president's chief of staff has tested positive for coronavirus, a source with direct knowledge said.

The illness of Abba Kyari, who is in his 70s, brings the disease into the immediate circle of 77-year-old President Muhammadu Buhari.

Kyari has a history of medical complications, including diabetes, and is the gatekeeper to the president. Many who wish to deal with Buhari must go through Kyari, including Nigeria's top politicians and businessmen.

He traveled to Germany in early March with a delegation of other Nigerian officials for meetings with Siemens AG. It is unclear if he self-isolated upon his return to Nigeria.

A presidency spokesman did not comment on whether Buhari has been tested. The president himself has undisclosed medical ailments, and spent five months in London for treatments in 2017.