Militants wearing army uniforms have killed 19 people at checkpoints on a road in Nigeria's Borno state.
The armed men reportedly stopped motorists on the road and ordered them out of their cars before shooting them or hacking them to death.
Witnesses told the BBC the men were from Boko Haram, though the Islamist militant group has not yet commented.
North-eastern Nigeria is under a state of emergency as Boko Haram attempts to create an Islamist state there.
The group targets both the military and civilians, including in schools, and frequently clashes with the Nigerian armed forces.
The latest attack happened early on Sunday morning near the town of Logumani, not far from the Cameroon border.
'On the prowl'
Survivors said the gunmen were dressed as soldiers and were riding motorcycles before they ambushed their victims.
"We were asked to get out of our vehicles and lie face down by nine men dressed as soldiers who blocked the road," one man, who gave his name as Buba, told the AFP news agency.
"They shot dead five people and went about slaughtering 14 others before someone called them on the phone that soldiers were heading their way," he said.
He said the attackers then fled into the bush on their motorcycles.
Another survivor, Adamu Mallam, said he had heard the man next to him being killed with a knife.
Buba said he knew the attackers were from Boko Haram because they had beards, which soldiers do not.
"Everyone in this area knows Boko Haram is on the prowl, raiding villages and attacking vehicles. It has become a common occurrence," he said.
The BBC's Nigeria correspondent, Tomi Oladipo, says the army often sets up checkpoints on roads in the troubled region to stop the militants, and it could be that the gunmen copied the tactic to catch their victims unawares.
Boko Haram has waged a deadly insurgency since 2009 in its bid to create an Islamic state in the mainly Muslim north of religiously mixed Nigeria.
It has been blamed for many violent attacks which have claimed the lives of nearly 2,000 people since 2011.
The group's name translates as "Western education is forbidden", and it has carried out several attacks on schools and colleges, seeing them as a symbol of Western culture.
Last month, up to 50 students died when suspected Boko Haram militants attacked an agricultural college in the north-east.
The Nigerian military said in August that it might have killed the group's leader, Abubakar Shekau, in a shoot-out.
However, a video released last week purportedly showed him alive.
Other previous reports of his death later proved to be unfounded.