Much of the Chadian force fighting Boko Haram in Nigeria has withdrawn to Cameroon and is deploying farther south, Chadian soldiers and a Cameroonian military official said on Thursday, signaling the potential start of a new offensive.

Chad's military has spearheaded an operation by Nigeria's neighbors against the Islamist militant group that has killed thousands in northeast Nigeria and in recent months mounted an increasing number of cross-border raids.

Nigeria has simultaneously launched an offensive to retake a series of towns with the backing of hundreds of mercenaries from South Africa and the former Soviet Union in a bid to secure towns ahead of a rescheduled March 28 election.