Diplomats check reports of Nigeria hostages' deaths
Diplomats are investigating claims that seven foreign hostages seized last month in Nigeria have been killed.
A statement posted on the internet from Nigerian militant group Ansaru said it had killed the hostages.
The hostages - from Britain, Greece, Italy and Lebanon - were seized in the northern state of Bauchi.
Ansaru, which emerged last year, is suspected of being an offshoot of the Boko Haram Islamist network.
The message from Ansaru included photographs purporting to show a gunman standing over at least one body, although these could not be verified.
The UK Foreign Office said it was aware of the reports and was "urgently investigating".
The seven hostages were seized in a raid from a construction site belonging to the Setraco company. The raid also resulted in the death of a guard.
Ansaru said the hostages were killed because of a rescue attempt by British and Nigerian forces. But British officials said they were not aware of any such attempt.
Last year there was a failed bid by special forces to rescue a British and an Italian hostage believed to be held by Ansaru. The pair were killed before they could be rescued.
Ansaru said it had carried out the latest kidnapping in revenge for what it called atrocities by European nations against Islam.Campaign of violence
The Ansaru movement has been listed by the UK government as a "terrorist organisation" aligned with al-Qaeda in the Islamic Maghreb.
The first attack for which it claimed responsibility was an attack on a police station in Nigeria's capital, Abuja, in November 2012.
The group has warned it will target non-Muslims "in self-defence".
Extremist groups operating in the north of Nigeria have intensified a campaign of violence in recent years.
Seven French nationals are still being held after they were kidnapped across the border in Cameroon by gunmen believed to be members of Boko Haram.