Persistent reports in recent days indicate that Russia is increasingly involved in the civil war in Syria. The involvement is stealthy and apparently not as heavy as in eastern Ukraine, but it creates interesting prospects for U.S.-Russian relations, as well as for the development of both the Syrian and the Ukrainian conflicts.

The evidence of Russian activity is sketchy. There’s a video from Syrian government forces showing a Russian BTR-82A armored personnel carrier firing shells, apparently during a battle near the port city of Latakia, which is strategically important to the regime of Syrian President Bashar Assad. Russian commands (“More! Do it again!”) are heard vaguely in the background.

There’s a report on an Israeli website claiming a Russian “expeditionary force” is already in Syria and the Russian air force was about to start attacking Islamic State targets.

There’s a post on a Bosphorus ship-spotting blog with photographs of the Russian landing ship Nikolai Filchenkov carrying tarp-covered military machinery south.

There’s a story in the pro-Assad Syrian newspaper Al-Watan saying that Russia was discussing the construction of a military base in Syria.

And there are numerous traces of Russian military personnel’s presence in Syria on the social networks: servicemen’s wives worrying about their husbands’ postings to Syria, the husbands themselves taking selfies with posters of Assad and Russian President Vladimir Putin in the background.

The official denials are not just predictable but also less vehement than those of Russian involvement in Ukraine. “It’s too early to say we are ready to do it,” Putin said last week when asked whether Russia was willing to take part in the fighting in Syria. “We are already providing serious support to Syria with armaments and military training.”

This has the U.S. worried. Secretary of State John Kerry has called Russian Foreign Minister Sergei Lavrov about it (and was told that Russia was not stepping up its military presence, just arming the Syrians, something it has never tried to conceal). The U.S. has also asked Greece to close its airspace to Russian flights carrying supplies to the Assad regime. The request is now being considered.

There’s enough noise about the increased Russian presence in the Latakia area for Russian media to speculate about a “second hybrid war” and “getting bogged down” in Syria as the Soviet Union did in Afghanistan and Putin’s Russia did in eastern Ukraine.

The commentators describe the putative Russian intervention as a Putin gamble. The Russian leader travels to the United Nations General Assembly next week, and there, they speculate, he may offer the U.S. a deal: Russian aid to the anti-Islamic State effort in Syria in exchange for concessions on Ukraine and an end to sanctions.

“Moscow, which, unlike Washington, doesn’t have to deal with resistance from public opinion and Congress, is to undertake the destruction of ISIS,” Kirill Martynov wrote in Novaya Gazeta. “If the plan succeeds even partially, the Russian authorities will get all they could ever dream of — the normalization of relations with the West, the prospect of negotiations on the status of Crimea and, at the same time, a demonstration of Russian power throughout the world: Unlike the indecisive Western democracies, we are able to attack terrorists even in the Middle East.”

It’s hard to see the Kremlin harboring any such naive dreams. After years of backing anti-government rebels, the U.S. is highly unlikely suddenly to support a Russian effort to prop up Assad. Moscow has long portrayed him as the lesser evil in the Syrian conflict, but the governments taking part in the U.S.-led anti-Islamic State coalition — including Saudi Arabia and the United Arab Emirates — have never bought it.

To them, Iran-backed Assad is almost as bad as the Islamic State fanatics. Tactically, the U.S. might benefit from Assad’s success against Islamic State, but it won’t back him publicly or make any long-term bets on his success.

Washington’s official position was recently expressed by State Department spokesman Mark Toner: “There’s a 37-some-odd-country coalition that’s taking the fight to ISIL [Islamic State]. We would welcome Russia to be more involved in that effort.” At the U.N., Putin may call for reformatting the coalition, but he can’t hope for a positive response, much less for a reward in the form of reduced sanctions.

That doesn’t mean, however, that Putin is not contemplating deeper military involvement in Syria. The “demonstration of power” idea must be tempting. Russian troops have only proven their effectiveness in small local conflicts recently — the swift operation against Georgia, the bloodless occupation of unprotected Crimea, a couple of successful battles against a weak Ukrainian military. A success where, as Putin noted last week, the U.S.-led campaign of airstrikes is failing to stop the advance of Islamic State would advertise Russia as a force to reckon with outside its home region. On the other hand, allowing the anti-Assad forces — Islamic State or other rebel groups — to seize Latakia and then perhaps the small Russian naval base in Tartus would suggest Russian weakness, something Putin hates to allow. The facility, which in peacetime had just four Russian naval personnel taking care of occasional vessel repairs, now appears to house hundreds of marines arriving on ships such as the Nikolai Filchenkov.

Putin doesn’t really need a deal with the U.S. to step up that presence. All he requires is quiet on the Ukrainian front to free the Russian military from distractions — and indeed, in recent days, all fighting there has stopped, as if by magic. Ukrainian President Petro Poroshenko even said last week that the Minsk cease-fire agreement was truly being observed for the first time since it was signed in February.

Going into Syria would be the same kind of bold move as the Crimea annexation: Putin would try to win first and negotiate later. Many of the servicemen being sent to Syria now are from Crimean bases. The difficulty is that Islamic State is not the cowed, disorganized Ukrainian military of March 2014. It has repeatedly proved its military prowess both against Assad’s forces and the Western-trained Iraqi army. Russian generals may be telling Putin they can beat Islamic State, but then Soviet generals also told Leonid Brezhnev in 1979 that they could overrun Afghanistan.

Going in without international support would be a huge risk. “I have no doubt that military intervention in Syria would be an adventure that would put Russia in mortal danger,” Yevgeni Kiselyoev, a former top TV anchor in Moscow who now lives in Kiev, wrote in a blog post.

If Putin does decide to wade into battle, it will prove more vividly than the aggression in Ukraine did that he is indeed an adventurer, not a pragmatist. Relying on military operations to prop up his popularity when the economy is going through a bad patch is far from a fail-safe strategy, especially with Islamic State as an opponent and the U.S. loath to lend support.

If, on the other hand, Putin holds back, confining himself to arms supplies and training for Assad’s troops, Russia’s neighbors — perhaps excluding post-Soviet states — can heave a sigh of relief. Such a pragmatic decision would mean Russia is resigned to its status as a regional power without Napoleonic expansionist ambitions.

Based in Berlin, writer Leonid Bershidsky is a Bloomberg View columnist and the author of three novels and two nonfiction books.