Two Americans and two Canadians kidnapped at gunpoint in Nigeria

Nigeria police detain suspicious people April 28, 2011 near a polling station in Bauchi, northern Nigeria.

Lagos, Nigeria (CNN)Two American and two Canadian citizens have been abducted by unknown gunmen in Kaduna, a state in Northern Nigeria, a spokesperson for the Kaduna State Police told CNN.

Mukhtar Aliyu, spokesperson for Kaduna State Police, said that the two men were abducted on Tuesday at 7p.m. local time, while traveling with police escorts from Kaduna city to Abuja.
"The abductors ambushed them along with police escorts who traveled with them, two policemen were killed in the gun battle," he said.
    Aliyu told CNN that the foreign nationals were members of an investment team for a solar power project in Kafanchan district in Southern Kaduna.
      No ransom has been demanded neither has the police been contacted, he added.
      Authorities said all necessary measures were being taken to locate them, while anti-kidnapping security agencies have mounted surveillance on the Kaduna-Abuja Expressway, the road that links the two states.

      Frequent abductions

      The US State Department had warned against travel to Kaduna and seven other states in north Nigeria due to frequent incidents of robberies and abductions along the Kaduna - Abuja highway last year.
        Kaduna is among nine other states targeted by Boko Haram, a terrorist group in northeast Nigeria, it said.
        The state department said, "Due to the risk of kidnappings, robberies, and other armed attacks, US citizens should also avoid all but essential travel to: Bayelsa, Delta, Kaduna, Katsina, Plateau, Rivers, Sokoto, and Zamfara states."