COTONOU, Benin — Militants inflicted heavy losses on Benin’s armed forces during an attack this week on a fortified military post in the north of the country, authorities said, raising further concerns from analysts about the expansion of jihadis into West Africa’s coastal states.

Col. Faizou Gomina, the national guard chief of staff, said in a statement that the attack took place on Wednesday and offered his condolences to victims, without naming the attackers or giving the number of casualties.

“We have been dealt a very hard blow but we will not give in,” he said.

While no group has taken responsibility for the attack, Benin has for years faced spillover violence in its north from Sahel countries like Burkina Faso and Niger in their battle against Islamic extremist groups.

The tri-border area has long been a hotbed for extremist violence, primarily concentrated around the W-Arly-Pendjari Complex. This large national park spills over into all three countries and has become a launching pad for cross-border attacks by militants.

The attack happened in an area where the al-Qaida-linked JNIM jihadi group is known to be active and shows that the rebels are “actively and violently confronting the Beninese (security) forces,” said Kars de Bruijne, a security analyst and senior research fellow at the Clingendael Institute think tank.

“It basically shows … an infiltration and expansion of JNIM into Benin,” Bruijne added.

The attack also raised further concerns about joint security efforts in West Africa, whose regional bloc known as ECOWAS recently split. The group suffered a major setback last year with the withdrawal of the three coup-hit, conflict-battered nations of Niger, Mali and Burkina Faso, a move analysts say makes it more difficult for non-existent regional efforts to materialize.

The JNIM group has been one of the most active jihadi groups in Africa’s Sahel region. Analysts have warned the group is looking to expand to safer coastal West African states like Benin and Togo, as a hub to rest, recuperate, get financing and gather weapons.