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An international charity says six of its aid workers who were kidnapped in Nigeria last week have appeared in a video.

Action Against Hunger says the six - comprised of one staff member, plus drivers and health workers employed locally - are "apparently in a good condition of health".

It is urging captors to release them.

The video, seen by the ����ý, shows one of the aid workers wearing a blue hijab.

Surrounded by five men believed to be her colleagues, the woman says her name is Grace, and calls on the Nigerian government and international community to intervene.

No group has claimed responsibility for the abduction but it is suspected to be the work of Islamist insurgents.

There are two main groups active in north-eastern Nigeria where the abduction happened - Boko Haram and the rival Islamic State of West Africa Province (Iswap) group.

Earlier this week, Action Against Hunger released a statement saying a convoy of its vehicles on the road to Damasak, in Borno State, had been attacked. It said one of the drivers was killed, and the rest of the team were missing.

"These are humanitarian workers who chose to devote their lives to helping the most vulnerable," .

The Nigerian military says it has cracked down on the Boko Haram insurgency, and the government claims the militants have been largely brought under control.

But the ����ý's Chris Ewokor in Abuja says militant groups are still active in Nigeria and continue to carry out attacks with devastating consequences in the region.