U.S. forces attacked a Russian military base in Syria, a top military official alleged on Thursday.

Deputy Defense Minister Alexander Fomin claimed that the United States used a swarm of unmanned aerial vehicles to target an airbase in the Latakia region of eastern Syria. The facility is a key launchpad for Russian military operations in the country over the last three years.

"Thirteen drones moved according to common combat battle deployment, operated by a single crew,” Fomin said, per state-run media, while traveling in Beijing. "Manual guidance is carried out not by some villagers, but by the Poseidon-8, which has modern equipment. It undertook manual control.”

Fomin’s remarks make explicit what Russia only had insinuated in January, when the incident took place. "Any suggestion that U.S. or coalition forces played a role in an attack on a Russian base is without any basis in fact and is utterly irresponsible,” a Pentagon spokesman said after the attack, according to a U.S.-backed media outlet.

The drone incident didn’t lead to any casualties, but an earlier attack on the base killed two Russian servicemen. “Taken together, the drone and mortar attacks appear to represent the most concerted assault on the Russian headquarters in Syria since the military intervention in September 2015, which has broadly succeeded in its goal of shoring up President Bashar al-Assad's fight to suppress the seven-year-old rebellion against his rule,” the Washington Post wrote at the time.

U.S. and Russian officials have maintained “deconfliction channels” to avoid conflict between their various forces operating in the Syrian theater. They also have demonstrated a willingness to downplay incidents. When U.S. forces repelled an attack on an American outpost reportedly assaulted by Russian mercenaries, the Kremlin minimized the number of casualties — U.S. estimates put the total in the hundreds — and American officials took a moderate tone when discussing possible Russian government involvement.

“[The Russians said] those are not our forces, and, at that time, it was confusing,” Army Gen. Jonathan Braga told NBC, while confirming that he was worried the fight would spark a larger conflict. “Absolutely concerned and that's why, again, I had a professional dialogue with our [Russian] counterparts throughout the night.”

Russia theorized that the U.S. had a technological motive for the drone attacks. "At the moment, when our air defense systems and electronic warfare measures were activated, the goal was to reveal this grouping and try to understand the parameters of irradiation and the combat modes of operation," Igor Korotchenko, editor of National Defense journal, told Kremlin-backed TASS.