"Three policemen have died as a result of a blast by a suicide bomber,"

Chechnya's interior ministry said in a statement.

The driver tried to speed into a police station in the town of Sernovodsk, about 50 kilometres (30 miles) west of Chechnya's capital of Grozny, but was prevented from doing so when a guard raised ground barriers, at which point the bomber set off his explosives, the statement said.

Three policemen died on the spot while four more were wounded, and the

blast damaged the building and created a "crater three meters wide and one meter deep," the statement said.

Russia fought two separatist wars in Chechnya over the past two decades,

with violence spreading to other regions in recent years.

The mountainous North Caucasus region, which includes Chechnya, is plagued by an Islamist insurgency, with near daily attacks on security officials.