ABUJA: Nigeria's President Goodluck Jonathan said on Monday that some of the seven hostages believed to have been killed by Islamist group Ansaru this month might actually still be alive and the government has been working to rescue them.

Ansaru said earlier this month it had killed the seven foreign construction workers it had been holding since February, posting a video of what it said was their bodies on the Internet, in what would be the deadliest single attack on foreigners in Nigeria since the 1960s Biafra war.

Italy and Greece confirmed that a Briton, an Italian, a Greek and four Lebanese abducted in northern Nigeria's Bauchi state had been killed by their captors.

Britain said only that it was likely they had been killed, whereas Nigerian authorities had so far not commented.

"Analysis of the information we have does not give us the conclusive position that they have all been killed but we suspect that some probably might have died of health related causes or direct killing," Jonathan said during a visit by Lebanon's President Michel Suleiman.

The kidnappings highlighted the growing risk posed by violent Islamist groups in Nigeria to Western interests.

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, especially since France launched an operation to flush them out of northern Mali in January.

"We have been working hard with friendly nations, especially the United Kingdom, to see that they are rescued. We suspect that they are in a rocky area, a very difficult area that can not be easily accessed but we are working hard to get to them," Jonathan said.

Ansaru killed a British and Italian hostage in northwest Nigeria during a failed rescue mission by British and Nigerian forces a year ago. They said that the latest killings were because of a rescue attempt, although Italy and Greece denied there was any such attempt.

The group claimed responsibility for the kidnapping in December of a French national, still missing.

Nigerian authorities are still looking for a French family of seven kidnapped in northern Cameroon and moved over the border by militants who said they were from the main Islamist insurgency Boko Haram.