Ukraine has admitted a rogue missile may have shot down a Russian airliner over the Black Sea.
It follows the recovery of suspicious fragments from the crash wreckage.
All 66 passengers and 12 crew members aboard the plane travelling from Tel Aviv to the Siberian city of Novosibirsk were killed.
Ukrainian officials have until now strongly denied accusations its military was responsible for the crash of a Tu-154 plane over the Black Sea last Thursday.
President Leonid Kuchma has admitted an accidental missile hit as the possible cause.
"This is theoretically possible, but there are lots of points that must be clarified," he said in Kiev.
But he promised to accept any conclusion the investigation comes up with.
A top Russian investigator said experts have found fragments resembling the missile's payload in bodies recovered from the jetliner's wreckage.
"Whatever the joint working group signs, I will agree with it," Kuchma said.
"Such things don't just happen in Ukraine ... mistakes happen everywhere," he added
US intelligence officials, based on spy satellite evidence, say the plane was hit by a Ukrainian S-200 missile during exercises on the Crimean Peninsula, which juts into the Black Sea.