The Chadian air force bombed the Nigerian town of Gamboru on Saturday, in an effort to drive out Boko Haram militants and allow troops from Chad to enter the northeastern town. Fighter jets then bombed areas around Gamboru, which is located near Lake Chad along the border with Cameroon, according to Agence France-Presse

The airstrikes by Chadian forces followed similar bombings earlier in the week intended to displace Boko Haram from parts of the country it has overtaken. Boko Haram seized Gamboru in Borno state several months ago, AFP reported. Chad deployed airstrikes and soldiers against Boko Haram in northern Nigeria on Thursday, which was the first foreign military intervention of its kind on Nigerian soil, according to the Associated Press.

The governments of Chad, Cameroon, Nigeria and Niger have all agreed to increase cooperation to stifle the terror threat — a conflict that has displaced more than 1 million people and killed tens of thousands in the last year, according to the Council on Foreign Relations, a U.S.-based independent think tank.

United Nations Secretary-General Ban Ki-moon gave his support Saturday to the African Union’s decision to send a regional five-nation force of 7,500 troops to fight the Boko Haram insurgency in northeastern Nigeria, where the terror group has declared an Islamic caliphate encompassing about 130 towns and villages, according to Amnesty International.

“I welcome the decision of the AU and regional countries to establish an MJTF [Multinational Joint Task Force] against Boko Haram,” Ban told AFP at the two-day AU Summit in the Ethiopian capital of Addis Ababa.

“They have committed unspeakable brutality. Those terrorists should be addressed with a regional and international cooperation. Not a single country, even the regional countries, can handle this alone,” Ban reportedly said of the Boko Haram militants, which have pledged loyalty to the Islamic State in Iraq and Syria. “The United Nations is ready to fully cooperate with the African Union.”