ABUJA — Britain advised its citizens on Wednesday against travelling to several regions in northern Nigeria, following an increase in attacks blamed on Islamist militants and the kidnapping of several foreigners earlier this month.

Gunmen killed a security guard and kidnapped a Briton, an Italian, a Greek and four Lebanese workers after storming the compound of Lebanese construction firm Setraco in Bauchi state on February 16.

It was the worst case of foreigners being kidnapped in the mostly Muslim north of Africa’s most populous country since an insurgency by Islamist militants intensified two years ago.

Britain upped its travel risk ratings on Wednesday, advising against any travel to Bauchi state and Okene city in southern Kogi state, where militants last month attacked Nigerian troops who were bound for Mali to counter an Islamist insurgency. It also advised "against all but essential travel" to Kaduna, Kano, Jigawa and Katsina states, a statement from the foreign office said.

Western governments are concerned the militants may link up with groups elsewhere in the region, including al-Qaeda’s North African wing Aqim, especially in light of the conflict in nearby Mali.

France sent troops to Mali last month to help oust Islamist rebels.

Islamist group Ansaru claimed responsibility for the Setraco raid in Bauchi and the Okene attack.

The Setraco raid was "based on the transgression and atrocities done to the religion of Allah by the European countries in many places such as Afghanistan and Mali," said the group, which has kidnapped other foreigners in Nigeria in the past.

Britain put Ansaru on its official "terrorist group" list in November, saying it was aligned with al-Qaeda and was behind the kidnapping of a Briton and an Italian killed last year during a failed rescue attempt.

The group’s full name is Jama’atu Ansarul Musilimina Fi Biladis Sudan, which roughly translates as "Vanguards for the Protection of Muslims in Black Africa".

It is believed to be a breakaway group from better known Islamist sect Boko Haram, which has killed hundreds in recent months.

Reuters