Nigeria's military finally revealed a death toll of 39 from a new series of extremist attacks on soldiers, while President Muhammadu Buhari on Wednesday declared that Boko Haram and Islamic State-linked fighters should be wiped "from the surface of the earth".Another 43 soldiers were wounded in five attacks between Nov. 2 and 18, the army announced after days of silence, blaming "large numbers of Boko Haram terrorists."Shocked by the deaths, Buhari backed off past declarations that Boko Haram has been defeated and urged the military to "rise to the challenge." He addressed security leaders in the turbulent northeast as he faces growing criticism ahead of next year's election over the failure to end what he called a "must-win war."The Islamic State West Africa Province, the largest IS-linked extremist group in Africa and a recent Boko Haram offshoot, claimed responsibility for the deadliest attack, a Nov. 18 assault on a military base in Metele. Concerns are growing that the group, which has killed two abducted health workers in recent months, is becoming more vicious.Buhari, a former military dictator from the north, seeks re-election after making the defeat of the nearly decade-old Islamic insurgency a central goal of his presidency. He told the military chiefs that "I will do everything within my powers to continue empowering you" and vowed to improve soldiers' welfare, to applause.But some angry soldiers later tried to disrupt Buhari's comments to troops, causing him to pause and look around after he urged them to "please maintain your loyalty to the country".* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook. Some soldiers weary of the dangerous counterterror operations have protested amid concerns that the global drop in oil prices has hurt funding for military efforts in Nigeria, one of Africa's top producers of crude.Buhari's high-profile visit to Maiduguri city, the birthplace of Boko Haram, included a visit to troops wounded in the Metele attack.The president also announced he was convening a meeting on Thursday in Chad of the heads of state of several nations in the vast Lake Chad region. The meeting will review the security situation and "enhance the capacity" of the regional multinational force combating Boko Haram, his office said.The military will put in place a "new proactive strategy" to counter the recent losses, the State House cited the army chief of staff, Lt. Gen. Tukur Buratai, as saying.But the extremists appear to have adopted new strategies as well. Nigeria's army in its statement late Wednesday noted "daring moves by the terrorists" in the past few months, with increased use of drones against military positions and "infusion of foreign fighters in their ranks."Boko Haram has killed or kidnapped thousands over the years, including the mass abduction of the Chibok schoolgirls, and forced scores of children into carrying out suicide bombings.Even as he acknowledged that the fight against Boko Haram and the IS-linked offshoot was not over, Nigeria's president told the security chiefs that "there has been remarkable improvement" since he took office in 2015."We remain committed to ending the crisis in the northeast and making the entire area safe for all," Buhari said. He also urged troops to remain nonpartisan and vigilant as the elections approach.