In the video - which has not been verified by the BBC - the gunmen can be seen flogging the hostages who are lying on the ground.

Most of them are men. Some women - who were shielding their children from witnessing the beatings - can be heard asking the international community to help secure their release.

Eleven hostages were freed last month and at least 40 are believed to be still in captivity.

The Nigerian government says it is against the paying of ransoms but correspondents say criminal gangs have collected huge sums of money in recent years from the frequent cases of kidnapping.