(Updates with police statement, one more dead, paras 1, 7)

NAZRAN, Russia, Aug 31 (Reuters) - A "terrorist" blast killed four police and injured one on Friday in Nazran, the capital of Russia's southern province of Ingushetia, which borders Chechnya, Ingushi officials said.

"It was a terrorist act," a duty officer at the regional prosecutors' office told Reuters by telephone.

The officer said a police patrol was dispatched in a jeep to check reports a Russian-made Lada car packed with explosives was parked next to the cultural centre in the town's centre.

"When police approached the Lada, it blew up," he said. "There was virtually nothing left of the Lada car.

"Three policemen were killed and two were injured." Russian news agencies later said one of the injured died in hospital.

The interior ministry initially said the blast was the result of a traffic accident. But it later called the explosion a "terrorist act".

"Information collected by investigators show there was an explosive device equivalent to 2 kg (5 lb) of TNT," Interfax news agency quoted a police spokesman as saying.

A series of recent attacks against officials and police, blamed on Islamist rebels, has heightened security fears in Ingushetia. Earlier this month 2,500 troops were sent to the region to support local security forces.

Security was especially tight ahead of the start of the school year in Russia on Sept. 1. A big school is located next to the scene of the blast.

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