Unknown gunmen on Sunday shot dead four people and injured several others in a raid on a Christian farming village in northern Nigerian Kaduna state, the police said.

The gunmen stormed Bitaro, a village in southern Kaduna state, killing four people and injuring others, Kaduna police commissioner Ballah Nasarawa said.

"Four people were killed in the midnight attack and several others were injured by the gunmen whose identity remains unknown," Nasarawa said.

Security has been beefed up throughout the state and police formations have been placed on the alert to forestall further unrest, he said.

"No arrest has been made but we are on the lookout for the gunmen," he said.

Tension has been high in the predominantly Christian southern part of Kaduna state following April's deadly post-election violence in the area which took sectarian dimension.

Hundreds of people were killed in the violence and thousands, mostly minority ethnic Hausa Muslims, were displaced, according to rights groups.

Since then, sporadic nocturnal suspected reprisal attacks on villages in the area by gunmen have continued.

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