Two Americans and two Canadians were kidnapped during an ambush by militants in northern Nigeria, a police spokesman told AFP on Wednesday.

The four foreigners were on their way to the capital Abuja on Tuesday night after leaving Kaduna town, where they were assigned “unidentified gunmen” and killed two policemen accompanying them, said Mukhtar Aliu, a spokesman for Kaduna state police.

He said that around 19:00 (1800 GMT), the kidnappers began “a heavy exchange of fire with the two policemen who accompanied the foreigners and died with regret.”

“Police have done everything in their power to save them,” he said. “All our means (including special anti-kidnapping units) were used to find them alive and arrest the kidnappers.”

But he gave no further details on the identity of the hostages.

A US embassy spokesman contacted by AFP declined to comment. The Canadian Embassy could not be reached immediately.

Nigeria has been facing a brutal Boko rebellion in 2009 to create a radical Islamic state in northeastern Nigeria in a conflict that has killed at least 20,000 people and displaced more than 2.6 million.

But kidnap-for-ransom is a recurrent phenomenon in Nigeria, where gangs usually target wealthy people and their families, and the hostage is released within days after payment is made.

In early November, British Foreign Secretary Ian Squire, who was kidnapped in Nigeria, was killed by the British Foreign Office and three others were released. The four were abducted on 13 October in southern Nigeria.