Several Nigerian soldiers were killed in an ambush by IS-affiliated jihadists on a military convoy in the country's conflict-riven northeast, security sources said.
Fighters from the Islamic State West Africa Province (ISWAP) opened fire with heavy machine guns and rocket-propelled grenades on the convoy as it travelled to the town of Gudumbali in Borno state on Monday, the sources said.
ISWAP has claimed responsibility for the attack, saying its fighters killed or wounded dozens of troops.
A security source said "the terrorists surprised troops with an ambush as they were heading to Gudumbali".
"We lost several soldiers, vehicles and weapons to the terrorists in the attack," said the source, who asked not to be identified.
The convoy was on its way to Gudumbali to reinforce coalition forces from Nigeria and Chad for a major offensive to liberate the town from the jihadists, said a second security source.
He added that the losses had been great and that from reports coming in, the number of casualties was "huge".
A third security source said: "It is not precisely clear the number of casualties recorded in the attack but a number (of troops) paid the supreme price."
ISWAP fighters ambushed the Nigerian army convoy and "clashed with them with a variety of weapons," the group said in a statement on Tuesday claiming responsibility, according to SITE Intelligence which monitors jihadist activities worldwide.
The group also claimed to have destroyed several trucks and captured numerous other vehicles in the attack.
Before soldiers withdrew from Gudumbali in December, ISWAP had repeatedly attacked troops in the town.
In December, ISWAP fighters carrying anti-aircraft guns attacked a base in the town, sparking a fierce firefight before the assault was repelled with aerial support.
ISWAP claimed it killed five soldiers in that attack.
In September last year the jihadists sacked the same base and temporarily took control of the town before withdrawing.
The IS-backed faction has targeted dozens of military bases since last year, killing scores of soldiers, part of a wider Islamist militant insurgency that has raged in Nigeria for a decade.
A decade-long insurgency in northeast Nigeria by Boko Haram has killed more than 27,000 people, displaced some two million, and spilt over into neighbouring countries.
While Boko Haram tends to hit softer targets, the splinter faction loyal to the Islamic State group has ratcheted up attacks against the military since last year.