At least 20 people were killed and 17 wounded in an explosion yesterday at a shopping centre in the northwestern Russian city of Ukhta, the emergency situations ministry said.There was no immediate official indication of the cause of the blast, although reports in Russian news agencies suggested a gas explosion.

"An explosion whose cause is unknown took place at 1.58pm Moscow time (0958 GMT) in a shopping centre housed in a two-storey brick building," a ministry spokesman said.

Six of the injured were in a serious condition. Another 30 people have been rescued from a subsequent fire in the building, the spokesman said.

However, Interfax news agency quoted the local prosecutor's office as saying that arson was to blame.

"There was no explosion. A container of flammable substance was thrown into the shop and a fire started as a result, causing a great quantity of deaths and injured," the official told Interfax.

The official said terrorism was ruled out and that the incident "rather resembles a business dispute." Other Russian news agencies quoted sources saying a gas canister may have caused the explosion.

"Given the characteristics of the destruction, a gas canister exploded," an unnamed police source told Itar-Tass. The state-run RIA-Novosti agency said that according to preliminary reports the shop at the centre of the blast was selling gas bottles.

PHOTO CAPTION

Russian firefighters inspect a damaged shop after a fire in the town of Ukhta, 1500 km (930 miles) north-east of Moscow, July 11, 2005. (REUTERS)