Seven foreign hostages were killed by Nigerian-based Islamist terror group Ansaru, the group announced Saturday.

The hostages - a Briton, an Italian, a Greek and four Lebanese, were taken on February 7 after terrorists used explosives to blast through the walls of the construction company where the foreigners worked.

The group issued a statement in Arabic and English on an affiliate of the Sinam al-Islam network accompanied by screen shots of a video purporting to show the dead hostages, SITE said.

"(We) announced the capture of seven Christians foreigners and warned that should there be any attempt by force to rescue them will render their lives in danger," the statement said.

"The Nigeria and British government operation lead to the death of all the seven Christians foreigners," it said.