Nigerian President Muhammadu Buhari has addressed the nation following three months of medical leave in the UK.
In a televised speech, Mr Buhari said he had followed events in Nigeria closely during his absence.
He was “distressed” by calls for the dissolution of Nigeria, he said, urging Nigerians to come together.
But the president failed to disclose what he was being treated for. It was his second spell of medical leave this year.
“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,” Mr Buhari said.
Nigeria’s unity was “not negotiable”, he added.
The president also made reference to ethnic violence in the country, blaming “political mischief-makers”.
Ethnic tensions – with some calling for a separate state in the south-east known as Biafra – surfaced during his leave, while the war against the Islamist militant group Boko Haram continued in parts of the north.
Buhari’s unhealthy start to 2017
19 January: Leaves for UK on “medical vacation”
5 February: Asks parliament to extend medical leave
10 March: Returns home but does not resume work immediately
7 May: Travels to UK for further treatment
6 June: Buhari’s wife says he is “recuperating fast”
19 August: Buhari returns to Nigeria