Around 40 soldiers Chad were killed in an overnight attack on a military base in the Lac ("Lake") border region with Nigeria, Chad's presidency said. 

President Mahamat Idriss Deby visited the site early on Monday and ordered a military operation "to pursue and track down the attackers to their last entrenchments," according to the statement.

The government did not specify who had attacked the army facility, or which forces had been mobilized to respond. 

However, the AFP news agency cited unnamed local security sources as saying "Boko Haram elements" were behind the attack. The source said the attackers took control of the base after launching their assault late on Sunday evening. They then allegedly stole weapons they could carry and burned vehicles equipped with heavy weapons before leaving. 

AFP also cited a senior Chadian officer, who it said had requested anonymity, as saying the unit commander was among those killed in the attack. 

"We have many casualties, yes, but the situation is under control and our forces are on the ground pursuing the enemy," the governor of the Lac region, General Saleh Haggar Tidjani, told the AFP. 

Boko Haram and offshoots like ISWAP active in area

The Lake Chad or Lac region has been repeatedly attacked by insurgencies including Boko Haram and the Islamic State in West Africa (ISWAP), which itself formed after breaking away from Boko Haram. 

The movement has its roots in predominantly Muslim northeastern Nigeria but its influence soon spread to the west of Chad and the north of Cameroon where the three countries' borders meet.

The International Office for Migration in June recorded more than 220,000 people displaced by attacks from armed groups in Lake Chad province.

Chad is also an important Western ally in the regional fight against Islamist terrorism in the Sahel region, with its significance rising with other countries in the area turning their backs to the West. 

Mali, Niger and Burkina Faso have all ended military operations with the US and France in recent years and turned to Russia for support instead in the aftermath of military coups. 

Chad intensified military operations against Boko Haram and other jihadi groups after an attack in March 2020 that killed roughly 100 soldiers in the area. 

Longstanding President Idriss Deby was said to have died fighting on the front lines in 2021, aged 68, with his son Mahamat Idriss Deby, a senior general, taking power.

msh/dj (AFP, Reuters)