Seven foreign workers have been seized and a security guard shot dead by gunmen who attacked a construction company site in northern Nigeria, officials say.One of the workers seized was Italian, one was Greek and two others Lebanese.But UK officials could not confirm a report that another was British.No-one has admitted the abductions but the Islamist militant group, Boko Haram, has staged a series of attacks in northern Nigeria.A security guard was killed as the attackers targeted the workers' camp at Jama'are in Bauchi state.Correspondents say it is the biggest kidnapping in northern Nigeria in recent times.However, there have been a number of smaller incidents in the region, including the kidnapping of a French national, Francis Colump, in the northern state of Katsina.That abduction was claimed by a second militant group, Ansaru, which emerged in June 2012.The kidnapping of foreigners and wealthy Nigerians is common in the oil-rich Niger Delta region, in the south of the country, and has become a lucrative trade for criminals.Oil workers and other foreign nationals are often targeted because companies pay high ransom money to secure their employees' release, correspondents say. Police station attackedLebanese foreign minister Adnan Mansour said two of those held were from Lebanon.An Italian and a Greek national were also abducted from the site run by Lebanese-owned firm Setraco, the foreign ministries in Rome and Athens confirmed.Another of those seized was a Filipino, a union leader at Setraco told the BBC.The Italian ambassador in Abuja said, "Italy's absolute priority is the safety of its compatriot," Ansa news agency reported.A UK foreign office spokesman said it was investigating reports of a Briton being kidnapped.The raid was preceded by an attack on the local police station, when two vehicles were blown up, in the town of Jama'are, some 125 miles (200km) north of the state capital, Bauchi.The attackers then moved on to a camp belonging to Setraco, killing a guard and seizing the workers. Setraco is currently expanding a major road in the area.The state capital has itself been attacked several times by Boko Haram, which wants to impose Sharia (Islamic law) across Nigeria.Earlier this month, nine polio vaccinators were shot dead at two health centres in northern Nigeria.Some Nigerian Muslim leaders have previously opposed polio vaccinations, claiming they could cause infertility.Boko Haram has emerged as one of the most prolific militant groups in West Africa, carrying out a large number of low-level attacks but also some more sophisticated attacks.