Lagos - Nigerian military have thwarted attempted suicide attacks in the restive northeast, the epicentre of the seven-year Boko Haram insurgency, the army has said. Army spokesman Sani Usman in a statement late on Friday said that troops killed a suspected female suicide bomber a day earlier when she attempted to enter a military site in Yamtake in Borno state.Follow News24 Africa on Facebook and Twitter. "The failed suicide bombing attack was followed up with futile probing attack by terrorists which was decisively dealt with by the troops," he said. Usman said the troops killed all four attackers including two suicide bombers and recovered a cache of arms and ammunition, but one soldier was killed."Unfortunately, we lost a soldier in the process," he said. Boko Haram, which seeks to impose a hardline Islamic legal system in Nigeria's mainly-Muslim north, has killed at least 20 000 people and forced more than 2.6 million to flee their homes since 2009. A sustained counter-offensive with the help of a regional force has seen the Nigerian military retake swathes of territory from the insurgents, but the extremist group still poses a security threat to civilians. Boko Haram has recently stepped up suicide attacks and bombings in and around Maiduguri, the centre of the violence.