Soldiers from Chad and Niger crossed the border into Nigeria as part of an ongoing joint offensive against Islamist militant group Boko Haram, military officials confirmed Monday. The influx of new troops prompted major skirmishes between coalition forces and jihadists, according to witnesses.

Approximately 200 vehicles were used to carry the reinforcements across the border, according to the Associated Press. Chadian Brig. Gen. Zakaria Ngobongue declined to provide details on the operation’s specific objectives. “They are bandits and criminals who have nothing to do with religion,” he said. Nigerian military spokesman Brig. Gen. Chris Olukolade said “Nigerian forces were involved” in the offensive as well.

“They left in a huge convoy of over 200 vehicles, some of them fitted with machine guns, including armored tanks, ambulances, water tankers and cargo trucks, which indicate they were going for a prolonged operation,” a journalist who witnessed the departure told CNN.

Boko Haram has used Cameroon, which shares Nigeria’s northeast border, both to resupply its soldiers and to escape from multinational forces. As a result, coalition military leaders have directed soldiers from Niger and Cameroon to cut Boko Haram off from the border, while Nigeria and Chadian soldiers were tasked with engaging the militants directly, said Edgard Alain Mebe Ngo’o, Cameroon's minister of defense.

Nigeria, Cameroon, Chad, Niger and Benin agreed in January to form a task force of 8,750 soldiers to combat the threat posed by Boko Haram, which is responsible for the deaths of thousands over the last five years. Niger and Chad began their renewed offensive last weekend with air strikes and troop movements in northeast Nigeria, as coalition forces aim at stabilize northeast Nigeria ahead of the nation’s presidential elections later this month, according to Agence France-Presse.

The offensive came hours after Boko Haram leader Abubakar Shekau pledged his group’s allegiance to the Islamic State group, a fellow Islamist militant faction that gained control over vast tracts of Iraq and Syria last summer. Boko Haram was the 31st group to declare support for the group, which is also known as ISIS or ISIL, according to IntelCenter.