ABIDJAN (Reuters) - Three United Nations soldiers from Bangladesh were killed by an explosive device that detonated as they were escorting a convoy in northern Mali on Sunday, the West African country s peacekeeping mission and Bangladesh s military said.  Attacks on peacekeepers in Mali, where Islamist groups continue to operate in the vast desert in the north of the country, have made the U.N. mission there, MINUSMA, the organization s deadliest. Another five U.N. troops were seriously wounded in Sunday s explosion, which occurred at around 7 a.m. (0700 GMT) on the main road between the towns of Anefis and Gao, MINUSMA said in a statement.  Our thoughts go firstly to the families and loved ones. We pledge our complete support to them during this painful ordeal,  the head of MINUSMA, Koen Davidse, said.  The mission will use all means to ensure that justice is rendered.   The U.N. did not immediately release the nationalities of the soldiers. But the Bangladesh military s media department confirmed that three of its soldiers had died by an improvised explosive device during an encounter with militants, adding that four other Bangladeshi peacekeepers were injured in the attack. West Africa s arid Sahel region has in recent years become a breeding ground for jihadist groups   some linked to al Qaeda and Islamic State   that European countries, particularly France, fear could threaten Europe if left unchecked. Despite a 2013 French-led military operation that drove back militants who had seized control of Mali s north, the area remains home to groups that have staged assaults on high-profile targets in the capital Bamako, Burkina Faso and Ivory Coast. MINUSMA, established in the wake of the French intervention, has struggled to quell the unrest. The U.N. Security Council established a sanctions regime this month that allows the body to blacklist anyone who violates or obstructs a fragile 2015 peace deal signed by Mali s government and separatist groups. Anyone who attacks peacekeepers, hinders the delivery of aid, commits human rights abuses or recruits child soldiers could also face sanctions, including a global travel ban or asset freeze. 