(Adds murder details and police, emergency services quotes)

YEKATERINBURG, Russia, May 22 (Reuters) - Russian police opened a murder investigation on Thursday after finding four bodies in the Russian Urals city of Yekaterinburg.

Earlier, the police said the four had been killed in a gas explosion, but a spokesman said after investigation the police had found signs of violence on the bodies and a strong smell of petrol in the nine-storey apartment building.

"We have excluded a gas explosion as the main reason for the fire, because we got a strong smell of petrol. After a closer examination, we found signs of violence on the bodies and handed over the investigation to the police," emergency services spokesman Sergei Kucherov told Vesti television channel.

Investigators were at the building in central Yekaterinburg trying to identify the bodies, said a police spokesman.

"A criminal case has now been launched into the act of murder," said local police spokesman Valery Gorelykh. (Reporting by Natalya Shurmina; Writing by Dmitry Solovyov; Editing by Elizabeth Piper)

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