Top leaders from Chad, Nigeria, Niger and Cameroon were holding talks in N'Djamena on Thursday to discuss the recent escalation of attacks by Boko Haram jihadists in the Lake Chad area.Nigerian President Muhammadu Buhari and Niger's Mahamadou Issoufou flew into the Chadian capital where they were holding closed-door talks with Chad's Idriss Deby and Cameroon's Prime Minister Philemon Yang, an AFP correspondent said. The meeting, which began during the morning, was focused on "the security situation in Lake Chad", a strategic area where the borders of four countries converge and where there has been a worrying "resurgence" of attacks in recent months, a Chadian diplomatic source said. All four countries belong to the Lake Chad Basin Commission, an intergovernmental organisation which oversees the usage of water and other natural resources in the region but which has also been engaged in the fight against Boko Haram. The group began a bloody insurgency in northeastern Nigeria in 2009 that has since spread to neighbouring Cameroon, Chad and Niger, prompting a regional military response.In 2015, Boko Haram jihadists split into two branches, one of which is affiliated to the Islamic State (ISIS) group. In Nigeria alone, more than 27 000 people have been killed over the past nine years, and some 1.8 million people have been forced out of their homes by the violence. And since July, there have been at least 17 attacks on military bases in Nigeria, almost all of them in the region around Lake Chad, according to an AFP count.Earlier this month, ISIS claimed its militants had killed 118 people in five operations in Nigeria and Chad between November 15 and 21. In the most audacious attack on November 18, ISIS-allied Boko Haram jihadists killed at least 43 soldiers when they overran a base in Metele village near the border with Niger, although the survivors put the number at more than 100 dead. On Tuesday evening, jihadists raided another Nigerian military base in a village near Lake Chad, killing three soldiers. Local residents said their truck was armed with anti-aircraft guns. Nigeria's Buhari, who came to power in 2015 on the promise to end the violence, is under increasing pressure to act following the recent surge in attacks as he gears up to seek re-election in a February ballot. Visiting troops in violence-hit Borno State on Wednesday, Buhari said defeating Boko Haram was "a must-win war". He has come under attack for previously claiming the Islamists were "technically defeated". Since 2015, all four countries have been collaborating militarily as part of the Multinational Joint Task Force (MNJTF) which seeks to counter Boko Haram in the Lake Chad region.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.