* Aid organisation says driver killed, 6 missing
* UN official says 'disturbed' by reports of attack
* About 7.1 million people need humanitarian assistance
Six people are missing following an attack on an aid convoy in northeast Nigeria, an international aid organisation said on Friday with sources stating that it was carried out by Islamist insurgents who abducted survivors.
Action Against Hunger in a statement said one staff member, two drivers and three other health workers are missing after Thursday's attack on a convoy near the town of Damasak in the northeastern state of Borno in which one driver was killed.
The nationality and other details of those kidnapped was not immediately clear.
The case raises concerns about the targeting of humanitarian staff in the region's decade-long insurgency, triggered by Boko Haram militants.
"We are deeply saddened by this tragic incident as these colleagues are dedicated to providing life-saving assistance to individuals and families," Action Against Hunger said of the attack.
The latest attack comes nine months after Islamic State's West Africa branch executed a Red Cross aid worker who was kidnapped from another town in northeastern Nigeria in March 2018.
Around 30,000 people have been killed in the insurgency, during which militant group Boko Haram has sought to create an Islamic caliphate. And more than two million people have been forced to flee their homes.
The United Nations Humanitarian Coordinator, Edward Kallon, said he was "deeply disturbed by reports of an incident involving aid workers" and was concerned about their safety.
"These acts of violence affect the very individuals, families, and communities that we support, and deprive vulnerable people of vital services," he said.
Kallon said 7.1 million people still need humanitarian assistance as a result of the insurgency.
Boko Haram controlled a swathe of land around the size of Belgium until early 2015 but was pushed out of it by troops from Nigeria and neighbouring Chad, Niger and Cameroon.
Since then the group has continued to carry out attacks - primarily in the form of suicide bombings, gun raids and kidnapping for ransom.
Islamic State West Africa Province, a splinter faction which split from Boko Haram in 2016, has carried out a series of attacks on military bases over the last year.