* Al Qaeda linked group kidnapped seven foreigners last month
* Victims were a Briton, an Italian, a Greek, four Lebanese
* Islamist groups main threat to Africa's top oil producer (Adds army spokesman, interior minister, tribute, details)
By Tim Cocks
LAGOS, March 11 (Reuters) - A Nigerian Islamist group that killed seven foreign hostages it had been holding since February has posted a video of what it said was their bodies on the Internet.
Italian and Greek authorities confirmed on Sunday that a Briton, an Italian, a Greek and four Lebanese construction workers abducted in northern Nigeria's Bauchi state last month had been killed by their captors.
The killings - the deadliest single attack on foreigners in Nigeria in the 1960s Biafra war - underscored the growing risks to Western interests posed by Islamists in Nigeria, who intelligence officials say have forged ties with al Qaeda-linked groups in the Sahara desert.
Attacks by Islamists in northern Nigeria, most prominently Boko Haram, have become the main threat to the stability of Africa's top oil producer after militants in the southeastern oil fields agreed to silence their guns under a 2009 amnesty.
British Foreign Secretary William Hague said it was "likely" the hostages were dead, calling it "an act of cold blooded murder".
Nigerian police declined to comment and Interior Minister Aba Moro told the BBC Hausa service on Monday there was no confirmation the hostages were dead.
"As long as it remains unconfirmed, efforts will be made to ensure their rescue and security," he said.
A spokesman for Nigeria's Ministry of Defence said that since this was a diplomatic incident, the presidency would have to make a statement on it. The official spokesman of President Goodluck Jonathan was not immediately reachable.
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 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."
THREAT TO THE WEST
Western governments fear ties with groups elsewhere in the region are drawing Nigerian Islamists towards a more explicitly anti-Western agenda, like that of al Qaeda's north African wing.
French intervention to flush Islamist groups out of northern Mali has 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.
Kidnapping has been rife in Nigeria's oil-producing southeast, but the kidnappers release victims quickly after a ransom, whereas few foreign hostages in the north survive.
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. Italy named the Italian as Silvano Trevisan.
Vaughan's friends and his Thai girlfriend Orasa Arpornkaew posted tributes to Vaughan on Facebook. "You're always in my heart," she said underneath a picture of him.
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 on this.
A German kidnapped by an Islamist group in January 2012 was also killed later in the year during a raid on his location.
A French national is being also held by the group, while another family of seven kidnapped in northern Cameroon is being held by a group claiming to be Boko Haram.
Security officials say Ansaru split from Boko Haram in January 2012, after the latter launched a devastating attack on the city of Kano that killed 186 people, mostly Muslims.
They believe it to be closely linked, though. The group's full name is Jama'atu Ansarul Musilimina Fi Biladis Sudan (Vanguards for the Protection of Muslims in Black Africa). (Additional reporting by Isaac Abrak in Kaduna and Maria Golovnina in London; Editing by Alison Williams)