Chad has closed its border with Libya and declared the frontier region a military zone amid a "potentially serious threat of terrorist infiltration", its prime minister said.
The move came just weeks after the African Union's security chief warned that thousands of Islamic State (IS) fighters ousted from Libya by a four-month US bombing campaign could be planning a move into sub-Saharan Africa.
Albert Pahimi Padacke, the prime minister of Chad, said troops would be sent to the border region. "Some isolated groups have converged towards the south of Libya on the northern border of our country which is potentially exposed to a serious threat of terrorist infiltration," he said in a message broadcast on state television and radio.
"Given the threats to the integrity of our nation, the government has decided to close the land border with Libya and also to declare the region a military zone. By these two measures the government intends to deal with any eventuality likely to disturb the tranquility of our populations in these regions and to threaten peace within our borders."
Smail Chergui, the AU's security commissioner, addressed member states on the threat to Africa from the Islamic State in Algeria shortly before Christmas.
He warned that 2,000 to 2,500 IS fighters were regrouping after devastating U.S. airstrikes on their bases in the Libyan city of Sirte with a view to relocating to the troubled regions of the Sahel, the Horn of Africa and the Great Lakes.
Chergui said some IS fighters were of African origin and were already present in Yemen and Somalia.
"Our priority is to be able to gather information and intelligence about them, share with our partners, then develop a concrete regional and international cooperation to curb the imminent terrorism danger," he said.
Chad is a repressive regime presided over by Idriss Déby Itno for the past 26 years but it has become a key player in the regional military force set up to tackle Boko Haram, which has its base in neighbouring Nigeria but has also launched attacks over its borders.
Boko Haram declared its allegiance to IS some years ago and in late 2015 a breakaway faction of al-Shabaab in Somalia followed suit. West Africa is also plagued by several al-Qaeda affiliates, one of which has attacked hotels and resorts in Burkina Faso, Mali and Ivory Coast in the past 12 months.
The growing terror threat has also prompted the United States to significantly scale up its military presence on the continent. Official figures released last week revealed that Africa has seen the biggest grown of U.S. special forces operatives overseas than anywhere else on earth with troop numbers increasing from 1 percent in 2006 to 17 percent in 2016.
However some reports on the Libyan border closure hinted at an ulterior motive by the Chadian government: a military base belonging to a rebel group that in 2008 marched on N'Djamena to overthrow Déby was bombarded by regime forces a week before Christmas.
Ryan Cummings, director of South Africa-based risk management firm Signal Risk, said the timing of the announcement was questionable.
"The final battle for Sirte was eight weeks ago and as early as July there has been mass movement of IS fighters so the suggestion you are closing your border because of it is disingenuous," he said.
"However the threat of IS fighters leaving Libya is absolutely legitimate because there are IS affiliates in Tunisia, Egypt, Algeria and Niger that have not been as active and the concern is if IS combatants go into those neighbouring countries to prop up the existing groups you then very suddenly have highly-trained, battle hardened militants operating across the Maghreb."