US intelligence chief James Clapper warned lawmakers Wednesday that Sub-Saharan Africa had turned into a "hothouse" for extremists staging lethal terror attacks.

US intelligence chief James Clapper warned lawmakers Wednesday that Sub-Saharan Africa had turned into a "hothouse" for extremists staging lethal terror attacks.

Presenting an annual threat assessment, Clapper said America's spy agencies believed Sub-Saharan Africa would "almost certainly" experience more security turmoil in 2014.

"The continent has become a hothouse for the emergence of extremist and rebel groups, which increasingly launch deadly asymmetric attacks, and which government forces often cannot effectively counter due to a lack of capability and sometimes will," said Clapper, according to a prepared text.

He also said that countries in the Sahel region faced the threat of terror attacks due to their backing of a French military intervention in Mali launched a year ago.

"Governments in Africa's Sahel region -- particularly Chad, Niger, Mali, Mauritania -- are at risk of terrorist attacks, primarily as retribution for these countries' support to the January 2013 French-led international military intervention in Mali," he said.

The region also faced pressures from swelling youth populations and "marginalized" ethnic communities that are frustrated over a lack of government services and a lack of jobs.