The United Nations refugee agency (UNHCR) says more than 5,000 Nigerians have fled to neighboring countries to escape clashes between security forces and insurgents.
UNHCR spokesman Adrian Edwards says that since mid-January, more than 4,000 people from northeastern Nigeria have fled to Cameroon, with another 1,500 people fleeing to Niger.
In a briefing Friday, Edwards said refugees have recounted horror stories that include deadly bombings and fires set in their villages. He said the U.N. agency is urging neighboring countries to keep their borders open for Nigerians who may need international protection.
In May, Nigerian President Goodluck Jonathan declared a state of emergency and deployed additional troops to three northeastern states to fight Islamist militant group Boko Haram.
However, attacks in the region have continued.
On Friday, villagers in the northeastern Borno state said a pair of attacks by suspected Islamist extremists had left 18 people dead this week.
The first attack occurred on Tuesday. Witnesses say 10 people were killed and dozens of homes burned in a village near Maiduguri.
Villagers say a second attack in a nearby village, on Wednesday, left eight people dead.
There were no claims of responsibility for the incidents.
Maiduguri is the birthplace of Boko Haram, a shadowy group that is believed to be fighting for the creation of an Islamic state in northern Nigeria.
The group has been blamed for thousands of deaths since it began an uprising in 2009.