• Ukraine sent drones and drone operators to Syrian rebel forces, The Washington Post reported.
• Groups led by Hayat Tahrir al-Sham overthrew Bashar Assad's decades-old rule on Sunday.
• The Ukrainian aid played a modest role in toppling him, Western intel sources told the outlet.

Ukrainian intelligence supplied Syrian rebels with about 150 drones and 20 drone operators last month, shortly before the offensive that toppled Syrian dictator Bashar Assad last week, The Washington Post reported, citing sources familiar with Ukrainian military activities.

Ukraine's aid was sent four to five weeks ago by Ukrainian intelligence operatives as part of efforts to weaken Russia and its Syrian allies in the region, sources familiar with Ukraine's operations abroad told the Post.

Business Insider was unable to independently verify the report.

The military aid played a modest role in ousting Assad, Western intelligence sources told the outlet.

On Sunday, Syrian rebels led by the Islamist group Hayat Tahrir al-Sham overthrew Assad after a lightning two-week campaign that caught the world off guard and ended Assad's 24-year rule.

The Post's report would be in keeping with Ukraine's efforts to undermine Russia's influence abroad.

Earlier this year, The Kyiv Post published videos that it said showed Ukrainian special forces interrogating Russian mercenaries in Sudan, and special forces fighting side by side with Syrian rebels against Russian mercenaries and Assad's forces.

A source within Ukraine's military intelligence agency told the outlet in June that since the start of the year, Ukrainian operatives had supported Syrian rebels in inflicting "numerous" strikes on Russian military facilities in the region.

In September, the Syrian newspaper Al-Watan reported comments from Russian Foreign Minister Sergey Lavrov, who said Ukrainian intelligence emissaries in Idlib, in Syria's northwest, were conducting "new dirty operations" and recruiting rebel fighters there.

Last month, Alexander Lavrentyev, Russia's special envoy to Syria, told Russian state news agency TASS that Ukraine's Main Directorate of Intelligence was arming "terrorists" in Idlib and that Ukrainian specialists were present there.

Ukraine's intelligence services didn't immediately respond to requests for comment from BI.

Alexander Libman, a professor of Russian and East European politics at the Free University of Berlin, told BI that if Ukraine is confirmed to have sent drones and drone operators to Syria, it would be surprising given how "problematic" the situation is in eastern Ukraine.

"I am not sure Ukraine can gain a lot by engaging in these types of operations," Libman said. "Rather, it will simply waste resources it needs to fight the war on Ukrainian soil itself."

The collapse of Assad, however, could jeopardize Russia's military footprint in Syria, where it could lose control over the Hmeimim air base and the Tartus naval base.

Russia has used those bases to project power in the Mediterranean and into Africa, and as a counter to NATO's southern flank.

Satellite images taken earlier this week by Maxar Technologies, obtained by BI, show Russian aircraft still present at Hmeimim, but Russian warships no longer present at Tartus.