A Nigerian Islamist group that killed seven foreign hostages it had been holding since February has posted a video of their bodies on the Internet.
Italian and Greek authorities confirmed on Sunday that a British, an Italian, a Greek and four Lebanese construction workers abducted in northern Nigeria's Bauchi state last month had been killed by their captors.
British Foreign Secretary William Hague said it was "very likely" they were dead, calling it "an act of cold blooded murder". Nigerian authorities have thus far not commented.
The national police spokesman and a spokesman for police forces in Bauchi state both said on Monday they could not yet confirm or deny the killings.
The silent video published by the al-Qaeda linked group, Ansaru, and dated March 9 shows a gunman standing next to a pile of bodies, then a series of close-ups of their faces lit up by a torch.
It carries the Arabic title "The killing of the seven Christian hostages in Nigeria" although the religion of the captives was not clear.
A caption underneath says in Arabic and in English: "In the name of Allah Most Beneficent Most Merciful".
The workers were seized from the premises of the Lebanese firm Setraco in the remote town of Jama'are in Bauchi state.
About a week after they were taken, Ansaru said it had abducted them because of "atrocities done to the religion of Allah by the European countries in many places such as Afghanistan and Mali".
The British foreign office named the British hostage as Brendan Vaughan. An intelligence source in the Nigerian capital Abuja named the Italian as Silvano Trevisan, adding that he had been suffering from hypertension and heart problems.
Ansaru killed a British and Italian hostage in northwest Nigeria during a failed rescue mission by British and Nigerian forces a year ago. Italy and Greece both said there had been no attempted rescue of the foreign hostages this time around, although Britain has not commented.
Attacks by Islamist groups in northern Nigeria, most prominently Boko Haram, have become the main threat to the stability of Africa's top oil producer after militants operating in the southeastern oil fields agreed to silence their guns under an amnesty deal in 2009.
Western governments are concerned that Nigerian Islamists may be forging growing ties with groups elsewhere in the region, including al Qaeda's North African wing.
French intervention to flush Islamist groups out of northern Mali has greatly increased the risk posed by Islamists to Western interests in north and west Africa - a risk highlighted by the dramatic attack on an Algerian gas plant in January in which at least 37 foreigners were killed.
Ansaru declared itself a separate group from Boko Haram in January, although security officials believe them to be closely linked. Its full name is Jama'atu Ansarul Musilimina Fi Biladis Sudan ("Vanguards for the Protection of Muslims in Black Africa").