An unspecified number of Nigerian soldiers went missing after an attack by the Boko Haram in Gashigar, a northern Borno community that borders Niger Republic, the Army has said.

The Army spokesperson, Sani Usman, said the soldiers were attacked at their position at about 5:30 p.m. on Monday.

Mr. Usman, a colonel, described the attackers as “escaping remnants of Boko Haram.”

“The troops did their best to defend the location in vain. In the process, 13 soldiers sustained injuries while some are still missing in action,” he said.

The spokesperson said the troops suffered a “temporary setback” and had to withdraw from the location.

“However, the wounded soldiers have been evacuated and receiving treatment, while efforts are ongoing in search of those missing and clear the Boko Haram terrorists at the general area,” he said.

The Boko Haram insurgency in northern Nigeria has caused the death of over 20,000 people and displacement of millions of others.

The group recently engaged in negotiation with the Federal Government which led to the release of 21 of the over 200 girls kidnapped from Chibok in Borno State in April 2014.

Despite the negotiation and despite losing initially claimed territory to the Nigerian forces, the group still carries out attacks like that of Monday.