Seven foreigners, reportedly including a Briton, who have been kidnapped in northern Nigeria are being held by an extremist Islamist group with a record of hostage-taking and murder.

Ansaru, which is described as a jihadi organisation, on Monday claimed responsibility for Saturday's attack on a construction camp in the town of Jama'are, in Bauchi state.

Nigerian authorities have said the workers are from the UK, Greece, Italy, Lebanon and the Philippines. A blurred photo purporting to be of the foreigners was shown on Nigerian TV.

The Foreign Office in London said it was aware of the reports and was checking with the authorities in Abuja. The prime minister's office said the government's priority was to establish the facts about the case.

In response to a question about whether the UK would help in any rescue operation, a No 10 spokeswoman said: "I think that the Foreign Office will want to do what they can."

A guard at the construction camp was shot dead in the raid. According to reports, the raid was preceded by an attack on the local police station where two vehicles were blown up.

It is the worst foreign kidnap case in northern Nigeria since an insurgency led by the Islamist militant group Boko Haram and other organisations intensified nearly two years ago.

Ansaru, whose full name – Jama'atu Ansarul Musilimina Fi Biladis Sudan – means Vanguards for the Protection of Muslims in Black Africa, claimed responsibility for the kidnapping of a French national last December, citing France's ban on full-face veils and its support for military action in Mali as reasons for the abduction.

The group is thought to be a breakaway from Boko Haram and seems to have a sharper focus on global jihad rather than a domestic political agenda.

Last year UK special forces failed in an attempt to rescue Chris McManus, an engineer from Oldham who had been held hostage in northern Nigeria for 10 months. He and an Italian hostage, Franco Lamolinara, were executed by their kidnappers as Nigerian troops backed by a unit of the Special Boat Service launched an operation to free them.

In December more than 30 attackers stormed a house in the northern state of Kaduna, killing two people and kidnapping a French engineer working on a renewable energy project there.

Chinese construction workers have been killed by gunmen around Maiduguri, the north-eastern Nigerian city where Boko Haram was formed. In the most recent attack on foreigners, assailants attacked North Korean doctors working for a hospital in Yobe state, stabbing two to death and beheading a third. No group claimed responsibility for that attack.

Foreign embassies in Nigeria have issued travel warnings regarding northern Nigeria for months. Worries about abductions have increased with the French military intervention in Mali, as its troops and Malian soldiers try to force out Islamist fighters who took over that nation's north in the months following a military coup.

Last week the US embassy in Nigeria's capital, Abuja, put out a warning following the killings of polio workers in the northern city of Kano and the killing of the North Korean doctors. "The security situation in some parts of Nigeria remains fluid and unpredictable," the embassy said.