The UTair ATR 72-200 craft, carrying 43 people, tilted to its right side and then sharply left as it crashed shortly after takeoff from Tyumen in western Siberia on Monday.

"At the moment, on the basis of the materials received, the investigators consider the failure to conduct a de-icing procedure to be the most probable cause of the air crash," Russia's Investigative Committee said on its website.

It said witness statements from those responsible for de-icing the plane and video evidence from the airport's surveillance systems supported the suspicion. UTair officials declined immediate comment.

The head of Russia's federal air transport agency Rosaviatsiya, Alexander Neradko, had also said earlier that the plane had not been de-iced properly.

UTair has suspended flights of ATR 72-200s pending results of a separate investigation by the Interstate Aviation Committee, which looks into air crashes in 12 former Soviet republics.

UTair director Andrei Martirosov said, however, that the decision was made to reassure passengers and that there were no grounds for doubt so far that the plane was in a good technical condition.

UTair said the plane crashed while trying to make an emergency landing.

The federal investigators said the plane had notched up 35,000 flying hours since going into operation in 1992 and had not had a "serious" technical check since 2010.

ATR is an equal partnership between two major European aeronautics players, Alenia Aermacchi, a Finmeccanica (SIFI.MI) company, and EADS (EAD.PA).

The crash was the worst in Russia since a Russian-made Yak-42 slammed into a riverbank near the city of Yaroslavl after takeoff on September 7, 2011, killing 44 people and wiping out the Lokomotiv Yaroslavl ice hockey team.

Russia and the former Soviet republics had one of the world's worst air-traffic safety records last year, with a total accident rate almost three times the world average, the International Air Transport Association said.

Russia's transport sector is plagued by deadly accidents blamed on a combination of decrepit infrastructure, human negligence and corruption.

(Editing by Alessandra Rizzo)

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