MOSCOW — Russian investigators said on Thursday that they had found no evidence that an explosion occurred aboard a Russian military plane that crashed into the Black Sea, killing all 92 passengers and crew, but that they had not ruled out the possibility of a terrorist attack.

“It was obvious that the equipment worked abnormally,” the Russian transportation minister, Maxim Sokolov said, adding that it would be “up to experts to find out” why that happened.

The plane crashed Sunday en route to Syria after a refueling stop in the Russian resort city of Sochi.

In the aftermath, the Russian authorities stressed that they believed it was unlikely that an attack had brought down the jet, a Tupolev 154, but they made clear at the news conference on Thursday that they were leaving open the possibility.