Six Nigerian charity workers kidnapped in Borno state last week have appeared in a video where they begged for their lives.
The workers said their captors were from the local ISIS affiliate, which has executed humanitarian staff before.
Nigerian President Muhammadu Buhari said on Thursday that talks were taking place to negotiate the release of the hostages.
In a three-minute video shared online on Thursday, a woman who identified herself as Grace begged her employer and the Nigerian government to help free her and the five men kneeling behind her.
The Christian Nigerian said she worked for Action Against Hunger and she and her colleagues were being held by militants who called themselves "the Calipha".
The video was released through the same channels as previous footage from the ISIS-linked IS West Africa Province.
“I beg Action Against Hunger, we have families and some of us have children,” Grace said. “Please do something to release us.”
An Action Against Hunger spokesman declined to say what the organisation's policy was on ransom payments.
Grace also implored her government for help.
“We are Nigerians and we are also working for Nigerians," she said. "I’m begging the Nigerian government to please do something to see we are released.”
The six were kidnapped on Thursday last week when a convoy was attacked on the road to Damasak, a northern town on the Niger border in Borno State.
Gunmen fired on the convoy, killing a driver and taking the six hostages.
The aid workers were seen with their captors on the day of their abduction passing through the villages of Chamba and Gatafo, south-west of Damasak, villagers told AFP.
They are now believed to be held in a militant enclave on the shores of Lake Chad.
The charity identified the captives as “one staff member, two drivers and three health workers”, although in the video Grace said they were all staff.
"Action Against Hunger strongly requests that our staff member and her companions be released," the group said.
"They are humanitarians and health workers and they chose to dedicate their lives to support the most vulnerable communities in Nigeria."
The militants, a breakaway faction of the Nigerian militant group Boko Haram, swore allegiance to ISIS leader Abu Bakr Al Baghdadi in 2016.
Since 2009, Boko Haram has carried out an insurgency across north-eastern Nigeria, Niger, Chad and Cameroon.
More than 27,000 people have been killed and two million displaced by the conflict, which has prompted a US military response.
The kidnapping raises concerns about the safety of humanitarian workers in an area where 7.1 million people need aid because of the insurgency.
“These acts of violence affect the very individuals, families, and communities that we support, and deprive vulnerable people of vital services,” said Edward Kallon, the UN Humanitarian Co-ordinator.
The ISIS affiliate has repeatedly attacked military bases in north-east Nigeria.
Last October, the militants killed midwife Hauwa Liman, 24, after her employer, the International Committee of the Red Cross, refused to pay a ransom.
A month earlier, Boko Haram murdered another Red Cross midwife, Saifura Khorsa.
“Some ladies from the Red Cross were caught," Grace said, her voice breaking. "They asked to be released but because Nigeria didn’t do anything about it, they were killed.”
“I’m begging on behalf of those here. Please, Nigeria should not allow that to happen to us.”