- President returns after treatment in UK
- Pledges to tackle division and violence
- Does not address health question
In a brief, televised address, the president called for unity and pledged to tackle terrorism and security threats.
"I am pleased to be back on home soil among my brothers and sisters," said Buhari. "But I was distressed to notice that some of the comments, especially in the social media have crossed our national red lines by daring to question our collective existence as a nation."
"Nigeria's unity is settled and not negotiable. We shall not allow irresponsible elements to start trouble."
The comments were widely interpreted as a rebuke to separatists calling for an independent state of Biafra
in the South of Nigeria.
The President went on to list a series of security threats including Boko Haram, clashes between herdsmen and farmers, and sectarian violence "fueled by political mischief makers."
However, Buhari did not address the question of his health, which has been the subject of rampant speculation. Online activists have circulated the hashtag #ResumeOrResign in a bid to end what they see as damaging uncertainty.
There has been no official confirmation of what illness the president has been suffering from or the severity of his condition. Vice President Yemi Osinbajo has taken charge in his absence.
Buhari's speech swiftly became the top trending topic on Twitter in Nigeria, but much of the reaction focused on his illness.
Buhari has now resumed his duties as president. But questions about his condition are likely to continue until they are answered.