The United States on Wednesday said it is cutting some military aid to Cameroon over human rights concerns, after growing allegations of abuses by security forces, a significant step against a solid ally in central Africa that is gripped by fighting between the government and Anglophone separatists.

The US decision comes after videos circulated online last year showing Cameroonian security forces shooting and killing civilians, including women with small children strapped to their backs. The videos were documented by Amnesty International and global media outlets.

The top US diplomat for Africa, Tibor Nagy, said in December that he feared that separatist crisis could get much worse, and warned against a brutal response to extremism, saying it could lead to radicalization.

Cameroon also faces a deadly threat from fighters with the Boko Haram extremist group based in neighbouring Nigeria.

The United Nations has said some 430 000 people in Cameroon's Southwest and Northwest regions, have fled the fighting between security forces and English-speaking separatists, who seek independence from the largely French-Speaking country.