Boko Haram fighters attacked Nigerian soldiers early on Monday near the border with Niger in the jihadists' northeast heartlands, the army said. The militants struck as the troops were on their way to the border town of Damasak, a military source said. The army took the area back from Boko Haram last year but has struggled to hold it.The group allied to Islamic State had been fighting to carve out an Islamist caliphate in the region for at least seven years in a conflict which has displaced more than 2 million people and killed thousands."Boko Haram terrorists attack troops of 113 Battalion," army spokesman Sani Usman said in a brief statement. "The troops have been battling the insurgents since (the) early hours of today."The troops had been trying to establish a permanent base in Damasak as Boko Haram remains active in its hinterland, the source said.No further information was immediately available from the remote area which is largely disconnected from mobile phone networks.Boko Haram controlled a swathe of land in northeast Nigeria around the size of Belgium at the start of last year but was pushed out by Nigerian troops, aided by soldiers from neighbouring countries.The group has since stepped up cross-border attacks and suicide bombings against markets, bus stations and places of worship...