Militants from Islamic State West Africa Province said on Monday they had executed a senior Nigerian army officer captured during a deadly ambush on a military convoy, in what would mark an unprecedented escalation in the 16-year insurgency.

The convoy, led by Brigadier-General M. Uba of the 25 Task Force Brigade, was returning from a patrol near Wajiroko village in northeastern Borno state late on Friday when it came under sustained gunfire, the army said.

Four military personnel were confirmed killed.

The army spokesperson did not immediately respond to Reuters' request for comment, but an earlier statement denied reports that Uba had been abducted, describing them as "fake news" and urging the public to disregard unverified claims circulating online.

However, in a statement posted on its Amaq propaganda channel, ISWAP claimed responsibility for the ambush and said it had executed the army officer identified as a brigade commander following an interrogation. Reuters could not independently verify the claim.

Borno state remains the epicentre of Nigeria's war against Boko Haram and its splinter group ISWAP. Despite military offensives, insurgents have repeatedly overrun army bases and communities this year, retreating only after reinforcements arrived.

A recent surge in attacks has raised concerns over the safety of front-line troops and the effectiveness of counter-insurgency operations in the region.