Last month, the US and Niger struck an agreement on the status of US forces as the two nations "define precisely what kind of military presence we may have in Niger in the future", a spokeswoman for the US state department said.

BBC: Mali conflict: US deploys 100 troops to neighbour Niger

Wilson wrote that he told the CIA he could find no evidence to prove the Iraq-Niger connection nearly a year before President Bush referred to it in his 2003 State of the Union as part of the rationale for war with Iraq.

CNN: Sources: FBI quizzes Wilson, Novak

The three semi-desert states, which border Niger, Chad and Cameroon, are roughly the size of England or the US state of Illinois but have a population of just 10 million.

BBC: Boko Haram crisis: Nigeria air raids target militants

Novak, a syndicated columnist who is also a CNN contributor, wrote about the CIA's decision to send Wilson to Niger in February 2002 to investigate the claims, which later wound up in Bush's 2003 State of Union address.

CNN: Ex-Cheney aide pleads not guilty

According to some press reports the attack at Abiteye in Delta State was carried out by oil thieves angry that the military Joint Task Force in the Niger Delta is succeeding in its effort to stop illegal oil bunkering in the area, thereby jeopardising the livelihood of local bandits who often masquerade as militants.

ECONOMIST: A big rebel group in the Niger Delta calls off its ceasefire