In what is being characterized as the deadliest clash between Russian and American forces since the Cold War, U.S. airstrikes reportedly killed around 200 Russian "mercenaries" during a failed attack on a U.S.-held military base in eastern Syria last week.

The large number of casualties was first revealed by Bloomberg in a report on Tuesday that adds crucial details to last Thursday's news of fresh U.S. airstrikes in Syria, which outlets at the time said resulted in the deaths of "pro-Syrian government" fighters.

The Syrian government denounced the deadly U.S. airstrikes as "new aggression." No U.S. casualties have been reported.

While Russia currently appears to be downplaying the incident in an effort to keep tensions with the U.S. at bay and claiming the Russian military "had nothing to do with the attack" on the U.S.-held military base, the Kremlin took aim at America's "illegal presence" in Syria and accused the U.S. attempting to "capture economic assets" in a statement immediately following news of the airstrikes last week.

"It's not clear who was paying the Russian contingent" that was killed in last week's strikes, Bloomberg observes. "Reports in Russian media have said Wagner—a shadowy organization known as Russia's answer to Blackwater, now called Academi—was hired by Assad or his allies to guard Syrian energy assets in exchange for oil concessions."

Vladimir Frolov, a political analyst and former Russian diplomat, warned in an interview with Bloomberg on Tuesday that the deadly airstrikes could spark "an acute international crisis."

"This is a big scandal," Frolov said.

In a graphic, Bloomberg highlighted several recent incidents that have contributed to soaring tensions in Syria, including recent Israeli airstrikes in the country.

"Such clashes are just the latest indication of the expanded role played by outside powers," writes independent journalist Reese Erlich on the increasingly volatile situation and the perils of the presence of  U.S. troops in north-eastern Syria.