A knife-wielding man has wounded eight people in a Siberian city before being shot dead by police, Russian officials say.

The motive for the mid-day attack on a central street in Surgut on Saturday has not been determined, the regional branch of the Investigative Committee said.

Four of the wounded were in serious condition, state news agency Tass reported, citing regional health official Vladislav Nigmatulin.

Surgut, with a population of about 320,000, is an oil and gas-producing centre 2,100km (1,300 miles) north-east of Moscow.