Blast in Russian McDonald's injures six

ST PETERSBURG, Russia (Reuters) - An explosion caused by a suspected bomb in a McDonald's restaurant in Russia's second city of St. Petersburg on Sunday slightly injured at least six people, officials said.

City prosecutor Sergei Zaitsev told reporters the blast in the restaurant on Nevsky Prospect, the main thoroughfare, occurred at 8:30 p.m. (10:30 p.m. British time) and had been caused by an unidentified substance.

Earlier, a police spokesman told Reuters an unidentified device had caused the explosion.

Zaitsev said five women and one man had been slightly injured and were taken to hospital for treatment. Five of them, including the man, were later released.

Police said the man was a foreign tourist.

"I was walking past and heard a noise and then felt a shake in the air and saw a flash. I got scared. After a few seconds, people started running out," said Artur, a witness who would give only his first name.

A Reuters reporter at the scene said the ceiling of the restaurant had fallen in, its windows had been blown out and there were parts of the broken ventilation system and glass scattered over the pavement.

Anti-Moscow rebels linked to Russia's Chechnya region have mounted a spate of bomb attacks on civilians in Russia but there have been no major attack outside the turbulent North Caucasus region for more than two years.

A police source has said police are checking other McDonald's restaurants in St Petersburg for explosives.