New York - Boko Haram militants were unable to disrupt Nigeria's presidential election, a United Nations envoy said on Monday, but the group's allegiance to Islamic State insurgents shows it has an agenda that goes beyond Africa's top oil producer and biggest economy.Boko Haram, which has killed thousands and displaced some 1.5 million people during a six-year campaign to carve out an Islamist emirate, committed itself this month to Islamic State, which controls swaths of territory in Syria and Iraq."Boko Haram's recent allegiance to the Islamic State [ISIS] ... whether for publicity reasons or to tap into ISIS support, is of concern as it is gives a clear signal that Boko Haram's agenda goes well beyond Nigeria," Mohammed Ibn Chambas, UN envoy for West Africa, told the UN Security Council.Nigeria's armed forces and troops from neighbouring Chad, Niger and Cameroon have driven Boko Haram from most positions it controlled earlier this year, reversing militant gains that forced Nigeria to postpone a 14 February election until 28 March.Results from the election, potentially the closest contest since the end of military rule in 1999, were due to start trickling in on Monday.Chambas told the 15-member Security Council: "Boko Haram was unable to disrupt the electoral process." But he added that while Boko Haram has been weakened, it was still committing "horrendous acts" against civilians."Schools in northeast Nigeria are no longer safe places of learning, as many of them continue to be attacked, looted, and destroyed. Several schools in the areas targeted by Boko Haram in Cameroon and Niger also remain closed," Chambas said."We have also observed an alarming trend of children being used by the group as human shields," he said.The United Nations said more than 7 300 people have been killed by Boko Haram since the start of 2014, more than 300 schools have been damaged or destroyed and less than 40 percent of health facilities in the area are operational."The escalation of Boko Haram-related violence in the region continues to hinder access to people in desperate need of humanitarian assistance," deputy UN aid chief Kyung-Wha Kang told the council.The Security Council is negotiating a resolution - drafted by Chad, Angola and Nigeria - to back and fund a regional force to take on Boko Haram. The 54-nation African Union has already approved a force of 10 000 troops.