The attack took place during a routine patrol of an area in south-western Niger known to harbour Al Qaeda insurgents
Military operations continue after deadly attack on American and Niger troops
Military operations were underway on Thursday near Niger's border with Mali the day after an attack by unidentified assailants which killed three members of the US Army Special Forces and five soldiers from Niger, security sources said.
The attack, which also wounded two US soldiers, took place during a routine patrol in a part of southwestern Niger where there are known to be insurgents, including members of Al Qaeda in Islamic Maghreb (AQIM).
The officials said it was likely that the commandos, who were Green Berets, were attacked by militants from Al Qaeda in the Islamic Maghreb (AQIM).
The two wounded American soldiers were taken to Niamey, the capital, and are in stable condition.
US Africa Command said the forces were with a joint US and Nigerien patrol north of Niamey, near the Mali border, when they came under hostile fire. The American troops are in Niger to provide training and security assistance to the Nigerien Armed Forces in their efforts against violent extremists.
Nigerien, American and French troops were conducting military operations in the zone on Thursday, a Nigerien security source said. No further details were given. An official at Mali's defence ministry said Malian forces had reinforced their checkpoints along the border. According to a Nigerien diplomatic source, those who carried out Wednesday's attack came from Mali.
Extremist groups form part of a growing regional insurgency in the poor, sparsely populated deserts of West Africa's Sahel. They have stepped up attacks on United Nations peacekeepers, Malian soldiers and civilian targets after being driven back in northern Mali by a French-led military intervention in 2013.
Malian militant groups have expanded their reach into neighbouring countries, including Niger, where a series of attacks by armed groups led the government in March to declare a state of emergency in the southwest.
A relatively new militant group called Islamic State in the Greater Sahara has also claimed some recent attacks.
The White House said president Donald Trump was notified about the attack on Wednesday night as he flew aboard Air Force One from Las Vegas to Washington.