MOSCOW, Aug 26 (Reuters) - An Air China plane flying to

Beijing from London with 265 people on board made an unscheduled

landing in Siberia due to engine trouble, Russia's state

aviation watchdog said in a statement on Tuesday.

Flightradar24 showed that the Boeing 777 landed in Russia's

Nizhnevartovsk airport in western Siberia.

"While flying from London to Beijing, the crew of an Air

China Boeing 777-300 decided to land at an alternate airfield in

Russia," Rosaviatsia, Russia's civil aviation authority, said.

"The preliminary cause was a malfunction of one of the engines."

Air China had decided to send a reserve plane to

Nizhnevartovsk, Rosaviatsia said. It would arrive later on

Tuesday and fly the 250 passengers and 15 crew to Beijing, it

said.