MOSCOW, April 11  -- The plane crash in western Russia that killed Polish President Lech Kaczynski and other top Polish officials was not caused by technical problems, Russian investigators said Sunday.

Preliminary results of the deciphered "black boxes" of the plane confirmed that there were no technical problems with the plane, Alexander Bastrykin, head of Russia's Investigative Committee, told Prime Minister Vladimir Putin.

"The pilot was informed about complex weather conditions and, nevertheless, made a decision on landing," Bastrykin was quoted by the RIA Novosti news agency as saying.

Russian and Polish investigators are jointly probing the cause of the plane crash.

"A group in Moscow has started deciphering the cockpit voice recorder. The quality of the recording is satisfactory, and there is every chance to obtain accurate information about the flight," Russian Transport Minister Igor Levitin told Putin.

Putin and his Polish counterpart, Donald Tusk, on Sunday laid flowers at the site of the plane crash.

The Tupolev Tu-154 plane carrying Kaczynski and top officials hit the top of trees as it attempted to land in thick fog at a Smolensk airport Saturday morning, killing all 96 people aboard.