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.
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.
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.