Nigeria's president, Muhammadu Buhari gives first speech in three months, says the country's unity is not negotiable

Nigeria's President Muhammadu Buhari on Monday addressed the nation after more than three months of medical leave in London.

In a televised speech, Buhari thanked Nigerians for their prayers and said he was pleased to be "back on home soil among my brothers and sisters".

According to the president, he had followed events in Nigeria closely during his absence.

He said separatists calling for the breakup of Nigeria have crossed a red line and the country's unity is not negotiable. According to him, he was "distressed" by calls for the dissolution of Nigeria, and urged Nigerians to come together. 

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, Buhari said.

Nigeria's unity is settled and not negotiable. We shall not allow irresponsible elements to start trouble, he said, adding that some ethnic violence was "fuelled by political mischief makers.

Ethnic tensions have surfaced in the last few months amid calls for a separate southeastern Biafra state, while youths in the restive Niger Delta oil hub have called for independence and Boko Haram militants seek an Islamic state in the northeast.

Buhari, 74 returned to Nigeria on Saturday after a long absence that has led some to call for his replacement. In his absence, Vice president, Yemi Osinbajo acted in his stead.  

Nigeria is Africa's most populous nation with 180 million people, split roughly equally between Christians and Muslims and about 250 different ethnic groups.