Abuja - Nigerian President Muhammadu Buhari took to state TV on Monday in his first speech since returning from a long medical absence in the Britain in a bid to dampen mounting separatist tensions in the country.The 74-year-old, who received treatment for an undisclosed condition in London, looked thin as he read slowly from a prepared statement in which he also vowed to redouble the fight against Boko Haram jihadists."I was distressed to notice that some of the comments (in my absence), especially in the social media have crossed national red lines by daring to question our collective existence as a nation. This is a step too far," he said."The national consensus is that it is better to live together than to live apart," added Buhari, who returned to Nigeria on Saturday after more than 100 days away from the west African nation of 190 million people.'Terrorists and criminals' Nigeria is facing a number of breakaway movements, including the Indigenous People of Biafra led by fierce Buhari critic Nnamdi Kanu in the country's southeast which is dominated by the Igbo ethnic group.The group has become increasingly vocal in its bid to win independence in recent weeks, with Kanu previously appearing in images meeting a private army of young men.Arewa, a radical Muslim youth group in the country's north, has issued an October 1 deadline for all Igbo people to leave the region.Boko Haram jihadists have meanwhile been fighting a bloody insurgency in the country's northeast since 2009 in a bid to establish a hardline Islamic state, a battle that has so far claimed at least 20 000 lives and forced some 2.6 million others to flee their homes.Buhari vowed renewed energy for the fight against "terrorists and criminals", singling out Boko Haram, kidnappers and those responsible for ethnic violence."We will tackle them all," he said.'Back on home soil' The president left for the British capital on May 7 with his prolonged absence causing tensions back home, where calls grew for him to either return or resign.Buhari, who said he was "pleased to be back on home soil", also called on political leaders to set aside their differences in the national interest."Our collective interest now is to eschew petty differences and come together to face common challenges of economic security, political evolution and integration, as well as lasting peace among all Nigerians," he said.Buhari, a retired general who headed a military regime in the 1980s, has been dogged by speculation about his health since June last year when he first went to London for treatment. He then spent nearly two months in London in January and February and said on his return in early March that he had "never been so ill". Since August 7, there were a series of protests in Abuja demanding that Buhari return or quit if he was unable to go on. The rallies turned violent last Tuesday when mainly ethnic Hausa traders pelted protesters with stones, prompting them to abandon their daily vigils.