Azerbaijan Airlines said on Friday that preliminary results showed that one of its planes which crashed in Kazakhstan on Wednesday experienced "external physical and technical interference".

Russian aviation authorities said the Azerbaijan Airlines plane had hit a flock of birds. But some experts cast doubt on that account, pointing to footage showing apparent holes in the fuselage.

There was growing speculation that an Azerbaijani airliner was shot down by Russian air defense system. Russia had initially said it believed the plane hit a flock of birds, but a U.S. official says it may have been struck by Russian air defenses.