According to Western governments, Nigerian Islamist militant group Ansaru’s claims to have killed seven foreign hostages it seized last month are credible.
The hostages – from Italy, Britain, Greece and Lebanon – were captured in a raid on a construction site in the northern state of Bauchi.
In an online statement posted on Saturday, Ansaru said it had killed the captives.
Ansaru is suspected of being an offshoot of the Boko Haram network.
On Sunday, UK Foreign Secretary William Hague said a British construction worker, named as Brendan Vaughn, was “likely to have been killed at the hands of his captors, along with six other foreign nationals”.
“This is an unforgivable act of pure, cold-blooded murder, for which there can be no excuse or justification,” he added.
The Italian government issued a similar statement, while the Greek foreign ministry said: “The information we have shows that the Greek citizen is dead.”
Ansaru’s online message included grainy pictures purporting to show the bodies of the seven – a Briton, an Italian, a Greek and four Lebanese workers.
The group said they had been killed because of a rescue attempt by British and Nigerian forces.
In an online statement posted on Saturday, Ansaru said it had killed the captives in Nigeria
However, in its statement, the Italian foreign ministry said: “There was never any military attempt to rescue the hostages by any of the governments concerned.”
It added that the group’s actions “can have no explanation other than blind and barbaric violence”.
Britain’s military said its warplanes which were recently spotted in Nigeria’s capital Abuja had been there to carry soldiers taking part in the French-led operation in Mali – not to rescue hostages.
The seven hostages were seized in a raid from a site belonging to the Setraco construction company. It resulted in the death of a guard.
Ansaru said it had carried out the attack in revenge for what it called atrocities by European nations against Islam.
The group abducted French national Francis Colump in December in an attack on a compound in the northern state of Katsina.
In January Ansaru said it had carried out an attack that killed two Nigerian soldiers as they prepared to deploy to Mali, where French-led troops have been fighting Islamic militants.
Seven French tourists, including four children, have been kidnapped by gunmen in Cameroon, near the border with Nigeria, French President Francois Hollande has said.
Francois Hollande says they belong to the same family and were seized by a “known terrorist group based in Nigeria”.
The president added that the seven were probably taken to northern Nigeria.
He indicated that the Nigerian Islamist militant group Boko Haram may have been responsible.
“I see the hand of Boko Haram in that part of Cameroon, and that is worrying enough for us to mobilize,” Francois Hollande said.
He said everything possible was being done to rescue the family and warned other French nationals in northern Cameroon to avoid “exposing themselves”.
The family had been returning from a visit to Waza National Park when they were attacked by men on motorcycles, Cameroonian officials said.
The incidents come amid a French-led intervention against Islamist militants in Mali.
Seven French tourists, including four children, have been kidnapped by gunmen in Cameroon, near the border with Nigeria
At least eight French nationals were already being held by Islamist groups in Africa.
Boko Haram has staged many attacks across northern Nigeria in recent years, targeting churches, government buildings and the security forces.
Another Islamist group- Ansaru – is also active in the region.
On Sunday, Ansaru claimed the abduction of seven foreign workers in Nigeria.
Italian, British, Greek and Lebanese workers are thought to be among those held after an attack on a construction project in Bauchi state.
Ansaru also says it is holding a French national, Francis Colump, who was seized in the northern state of Katsina.
French and Malian troops have seized the key towns of Diabaly and Douentza from militant Islamists, France’s defence minister has said.
French warplanes have bombed suspected Islamist positions around both towns since France launched a military operation in Mali on January 11.
A column of French and Malian troops entered Diabaly, said an AFP news agency reporter with the soldiers.
France has sent some 2,000 troops to help Malian forces fight the militants.
It has called on West African countries to speed up the deployment of a regional force of more than 3,000.
An Islamist group in Nigeria has said it carried out an attack last week which killed two Nigerian troops as they prepared to deploy to Mali.
Ansaru said it targeted the troops because the Nigerian military was joining efforts to “demolish the Islamic empire of Mali”.
French and Malian troops have seized the key towns of Diabaly and Douentza from militant Islamists
Nigeria has pledged to send 1,200 troops to Mali, with the first 50 deployed on Thursday.
Togolese and Senegalese soldiers make up the remaining 100 troops already in Bamako, AFP reports.
Mali’s Islamist fighters fled Diabaly, about 400 km (250 miles) from the capital, Bamako, on Friday.
On Monday, French soldiers from the 21st Marine Infantry Regiment as well as parachutists and Malian troops entered the town after reconnaissance flights by Gazelle helicopters, according to an AFP reporter who was with the soldiers.
They had set out at dawn from the nearby government-controlled town of Niono.
French Defence Minister Jean-Yves Le Drian said that Diabaly was now under the control of French and Malian troops, AFP reports.
The central town of Douentza, about 800 km (500 miles) from Bamako, had also been recaptured, he was quoted as saying.
Army commanders had earlier expressed fears that Islamists fleeing Diabaly had planted landmines.
On Sunday, Jean-Yves Le Drian said France was seeking “total reconquest” of northern Mali.
“We will not leave any pockets of resistance,” he told French television.
The Islamist groups currently control a vast area in the Sahara Desert, larger than France.