The Russian military has finally offered an explanation for its mysterious, and brief, deployment of Su-57 stealth fighter prototypes to Syria in February.

The Su-57s conducted "practical" test launches of "promising multipurpose tactical cruise missiles," Russian defense minister Sergei Shoigu said during a May 25 address in Moscow.

But there are good reasons to believe Shoigu's explanation is a lie. The Kremlin seems determined to portray its stealth fighters in the best possible light as prospects fade for mass-production of the troubled warplanes.

Two of the Russian air force's twin-tail, twin-engine Su-57s spent two days at Hmemmem Air Base in western Syria, where Russia's main military contingent has been based since Moscow intervened in the Syrian civil war on the side of regime president Bashar al-Assad beginning in September 2015.

The deployment startled observers when it was first reported by social media users on the ground near Hmemmem. Warplane-maker Sukhoi has assembled just seven Su-57s for testing since the type's first flight in 2010. The plane, a rough analog to the U.S. Air Force's F-22 and the Chinese J-20, is apparently years away from being truly combat-ready.

The Su-57 currently lacks many of its planned electronics and sensors and has been cleared to carry only a few different kinds of munitions. The jets usually appear in public carrying dummy bombs and missiles that are strictly for display.

U.S. Central Command, which oversees U.S. and allied air operations in the Middle East and keeps close tabs on Russian flights in the region, was dismissive of the Su-57s' February visit to Syria. "The presence of any new Russian aircraft in the region does not affect coalition operations, nor do we see this as a danger to coalition aircraft," a command spokesperson told The Daily Beast.

Thus the Syria deployment appeared to make little sense until Shugoi's announcement three months later. The Su-57s went to Syria to "assess the combat capabilities... of military equipment being developed," Shugoi said.

The Russian defense minister presented a video depicting an Su-57 launching a cruise missile from its bomb bay. Analysts have identified the munition as a new, radar-evading version of the '90s-vintage Kh-59.

Shugoi implied that the missile-launch was part of a "special operation in the territory of the Syrian Arab Republic." It's unclear whether the purported operation included attacks on rebel or militant forces or civilians.

Nothing in the video proves that the launch took place in Syria and not at, say, some remote air force testing site deep in Russia's interior. Central Command told The Daily Beast that it could not confirm any missile launch by the Su-57s in Syria. The Russian defense ministry did not respond to an email requesting hard evidence of the alleged missile test.

Tom Cooper, an author and expert on Russian warplanes, said he is skeptical of Shugoi's claim. "It would be far too risky to test a new cruise missile in Syria," Cooper told The Daily Beast. "What if the missile gets lost? If it lands in Turkey? Or in Lebanon? Or in Israel?"

Furthermore, Cooper added, any aerial testing in Syria would expose new and presumably advanced weaponry to close inspection by nearby U.S. and allied forces. Conducting a missile trial over Syria is tantamount to boxing up the munition and shipping it "straight to the White House," Cooper quipped.

Pavel Podvig, an expert on the Russian military, told The Daily Beast it's "possible" Shugoi's description of a missile test over Syria is merely propaganda.

There's ample precedent for the Kremlin making inflated claims regarding new weaponry. In March, Russian president Vladimir Putin revealed several new and supposedly "invincible" weapons types, including a nuclear-powered cruise missile with virtually unlimited range. But in tests between November and February, the nuclear-powered munition traveled no farther than 22 miles before crashing, according to news reports.

There are obvious reasons for the Kremlin to lie about the Su-57s' activities during their brief foray in Syria. The Russian air force has struggled to complete the stealth fighter's development amid deep budget cuts. India had been subsidizing work on the Su-57, in the hope of eventually buying scores of the planes. But New Delhi quit the program in April, citing a host of technological shortfalls.

As its relationship with the Indians cooled, the Kremlin cut its total order for Su-57s to just a dozen planes through 2025. The United States, by contrast, buys scores of new F-35 stealth fighters every year. China declared its first squadron of roughly a dozen J-20s combat-ready in February, just seven years after the first of the planes took off on its inaugural flight.

Justin Bronk, a combat aircraft expert at the Royal United Services Institute, told Business Insider that Russia "desperately" needs foreign investment to continue work on the Su-57. In that context, a dramatic—albeit possible staged—missile test makes sense.

When it comes to Moscow's struggling stealth-fighter program, "everything is staged for show purposes," Cooper said. "And almost certainly in Russia."