Suspected Boko Haram extremists caused explosions which killed 37 people at a security checkpoint in northeastern Nigeria Tuesday, as extremists attacked a Cameroonian military base near the border with Nigeria, killing at least five soldiers, said officials and witnesses.

Twenty civilians and 17 extremists were killed at a roadblock near Biu in southern Borno state, said Muhammed Miringa, a member of a civilian militia who was at the roadblock. When a van stopped at the checkpoint an extremist attempted to set off a hand grenade. Soldiers shot at him and the bus exploded and other extremists fired from another bus, said Miringa.

Also Tuesday, a suicide bomber detonated a bomb at a restaurant located near a military check point in Potiskum town killing four, including the suicide bomber, while five other sustained serious injuries.

In Cameroon, hundreds of militants attacked a military base in Waza and looted and set fire to scores of homes in the area before escaping back to Nigeria on Monday, Col. Joseph Nouma told The Associated Press. Eight wounded Cameroonian soldiers were brought to a military hospital in the capital, he said.

The renewed cross-border violence came as heads of states from Central African countries were ending a meeting in the Cameroonian capital, Yaounde, to plan the creation of a joint military response to the growing regional threat posed by Boko Haram.

The 10 member states announced that they had contributed more than 50 percent of the $100 million needed to fight Boko Haram. They also called on Nigeria to cooperate by allowing the multinational joint task force to attack Boko Haram in Nigeria.

The Nigeria-based extremist group has fought a five-year insurgency against the government there, and recently began stepping up its attacks against neighboring countries after Cameroon, Niger, Chad and Benin agreed to contribute troops toward a regional military effort.

The violence has forced some 157,000 people to seek refuge in Niger, while 40,000 others have gone to Cameroon and 17,000 are in Chad, the U.N. said.

Almost 1 million Nigerians are internally displaced, according to the country's own statistics.