MOSCOW — A Russian military transport plane carrying 33 passengers and six crew members crashed on landing at an air base in Syria on Tuesday, killing all on board, the Russian Defense Ministry said.

Initial reports ruled out a terrorist attack against the aircraft, an Antonov An-26 transport plane, with technical failure being the likely cause, the Interfax news agency reported. All those on board were Russian military personnel, the ministry said.

“According to a report from the scene, the airplane was not fired upon,” the Russian Defense Ministry said in a statement, adding that an investigation into the crash had begun. The plane hit the ground more than 1,600 feet short of the runway at the Russian-operated Hmeimim Air Base, the statement said.

Russia has stepped up security at the air base and at a naval facility at Tartus on the Mediterranean coast after both came under a drone attack in early January. The drones were shot down before they caused any damage and there were no casualties, according to a statement on the military’s Facebook page.