Nigeria-based group Ansaru has said it has killed seven foreign hostages it seized on February 7 from a construction company in Nigeria, SITE Monitoring Service said.
The group issued a statement in Arabic and English on an affiliate of the Sinam al-Islam network accompanied by screen
shots of a video purporting to show the dead hostages, SITE said.
One screenshot showed a man with gun standing above several prone figures lying on the ground.
Ansaru, which has kidnapped other foreigners in the past, had blasted into the compound using explosives and abducted a Briton, an Italian, a Greek and four Lebanese workers, the largest number of foreigners kidnapped in the mostly Muslim
north since violence by armed groups intensified two years ago.
The group's full name is Jama'atu Ansarul Musilimina Fi Biladis Sudan, which roughly translates as "vanguards for the protection of Muslims in Black Africa".
In its statement, the group said it had decided to kill the hostages, taken from the compound of a Lebanese construction company in the northern state of Bauchi, because of attempts by Britain and Nigeria to rescue them.
"(We) announced the capture of seven Christian foreigners and warned that should there be any attempt by force to rescue them will render their lives in danger," the statement said.
"The Nigeria and British government operations led to the death of all the seven Christian foreigners," it said.
Ansaru was suspected of being behind the killing of a British and Italian hostage a year ago in northwest Nigeria and Britain's parliament has labelled it a terrorist organisation.
Clashes in the north
Meanwhile, Nigeria's army said it launched an operation in the northern city of Maiduguri, the bastion of armed group Boko Haram, that led to the deaths of 20 suspected fighters and two soldiers.
The soldiers on Friday stormed a location where some Boko Haram men were found and "we exchanged fire with them and about 20 of them died in the crossfire. We also lost two of our soldiers while three were injured," said army spokesman Lieutenant Colonel Sagir Musa.
"We have also arrested 25 Boko Haram terrorists," he added.
The operation took place several hours after Nigerian President Goodluck Jonathan left Maiduguri, on his first visit to the restive city since his election in 2011.
Maiduguri has been the epicentre of attacks that have left hundreds of people dead and Jonathan on Friday defended the deployment of soldiers to the region.
The military has been accused of firing on unarmed civilians and razing neighbourhoods following suspected attacks, while Maiduguri residents also face roadblocks and rolling curfews in several areas.
"We always tell the soldiers to conduct themselves" professionally, Jonathan said.