MOSCOW — It was a heroic and straightforward story, according to the Russian Ministry of Defense. It also wasn’t true, say military analysts and news reports.

Two Russian pilots were killed Friday in Syria when a Syrian Mi-25 helicopter was shot down by the Islamic State militant group near the city of Palmyra, the ministry said. The pilots were on a training mission when they received an urgent request to fight off an Islamic State offensive that threatened to capture an important, elevated position nearby.

“Crew commander Ryafagat Khabibulin made a decision to attack the terrorists,” the state-run Tass news agency quoted the ministry as saying, adding that the pilots had been nominated for military awards. “Owing to the Russian pilots’ correct actions, the terrorists’ attack was thwarted.”

Soon, video of the attack appeared on an Islamic State website. An explosion near the rear rotor sends the gunship into a tailspin, and it crashes into regime-held territory. Anonymous military sources quoted by Russian state media suggested that the helicopter was hit by an American-made TOW antitank guided missile, suggesting that the Islamic State had benefited from U.S. weapons deliveries to rebel groups.

But according to newspaper and expert reports, the helicopter was not an Mi-25 (the export version of Russia’s old Mi-24 attack helicopter), but Russia’s new state-of-the-art Mi-35M helicopter, which first appeared in Syria in December and, crucially, is operated only by the Russian military.

Along with Kalibr cruise missiles, the TOS-1A multiple rocket launcher and the Sukhoi Su-34 strike fighter, the Mi-35M is part of a high-tech deployment that has turned the Syrian conflict into a training ground for Russia's advanced weaponry. The gunship features advanced avionics and can carry more and heavier weapons than the Mi-24.

If the helicopter was an Mi-35M, it would indicate that the gunship was Russian, not Syrian, and probably on a combat mission, instead of a training run. The distinction would shed light on an ongoing dispute over Russia’s intervention in Syria: To what degree are Russian forces, including special forces and artillery, helping Syria’s battered military take back ground held by the Islamic State and rebel groups, including those backed by the United States?

On Monday, the Kommersant newspaper reported that military sources “claim that the reports [of the attack on the helicopter] concern not the old Syrian Mi-25, but the new Russian Mi-35M (several of which were deployed to Khmeymim in March 2016).” A military analyst with ties to the Russian Defense Ministry who asked not to be identified by name in order to speak candidly said that he also believed the helicopter was an Mi-35M, not an Mi-25.

The Conflict Intelligence Team, a Russian open-source investigating team that uses data from social networks to report on the Russian military, said the helicopter “had non-retracted landing gear and short wings, which are distinct features of a Mi-35M helicopter.” But the post also made a controversial claim: that the helicopter may have been downed by friendly fire rockets from a wingman.

“During combat, the leader could have gotten into the line of fire of the … helicopter that followed it a bit above,” the report said, noting that the gunship launched unguided rockets shortly before it was shot down. “This explains why [the Islamic State] did not publish a video of their missile launch.”

Jeremy Binnie of IHS Jane’s said it’s difficult to discern exactly what’s happening in the video, though in the frame after the explosion on the Mi-35’s tail rotor, there appears to be a jet of smoke shooting away from the blast, something he believes to be the remnants of the projectile moving past the helicopter. According to Binnie, this indicates that whatever hit the helicopter came from the front, not from the rear as the Conflict Intelligence Report claimed.

The impact location, Binnie said, is not what would be expected of a man-portable air-defense system, or MANPADS, strike. Most MANPADS are heat-seeking and lock onto their targets largest heat source, usually the engine. In this case, whatever took down the helicopter hit its tail rotor.

While it would be nearly impossible to discern what model of weapon was used to shoot down the helicopter in that type of situation, it is unlikely that an antitank guided missile of any sort hit the Russian helicopter, said Binnie, as they are designed to destroy much slower targets. Last year, a TOW was used by Syrian opposition forces to destroy a Russian helicopter; however, the helicopter was stationary after landing on a hillside.

“Even if it was an [antitank guided missile], immediately calling it a TOW seems like a deliberate attempt to cast negative assertions around a U.S.-approved program,” Binnie said.

Binnie added that it was also possible that the helicopter was hit by a lucky shot from a larger-caliber antiaircraft gun. The Islamic State has been filmed with everything from 14.5mm to 57mm antiaircraft guns mounted in the back of pickup trucks.

Gibbons-Neff reported from Washington.