The Russians will take advantage of any void left by U.S. troops leaving Syria, the top general overseeing military operations there warned this week, which would likely mean more support for the Assad regime's brutal policies.

Russia viewed President Donald Trump's December announcement that U.S. troops would leave Syria positively, Army Gen. Joseph Votel, head of U.S. Central Command, said Thursday.

"I think ... they looked at that [like] this is an opportunity to fill the void that -- that we had provided in the support to the partners that we work with on the ground there," he told members of the House Armed Services Committee. "So, they look to gain and perpetuate what the Assad regime is doing."

Russia has been sending troops to Syria since 2015. While there to fight the Islamic State group, Russia has also struck U.S.-backed rebel groups fighting back against Syrian President Bashar al-Assad's forces. Assad has used ruthless tactics to counter local rebel groups fighting against his regime, including chemical attacks on civilian areas that have killed children.

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Votel, who said he's under no set timeline to remove U.S. troops from Syria or Afghanistan, despite Trump's calls to end the wars there, said Russia stands to gain power and clout in the region. And that could have a real impact, regionally and globally.

"It puts Russia more in the driver's seat in terms of what that solution might be. And, of course, it solidifies their presence in the Middle East in this critical part of the Levant right here," he said, speaking of the area that includes Iraq, Syria, Israel, Lebanon and Jordan. "I think that is an important objective of theirs."

Russia's presence in Syria has complicated an already-complex fight. Since they're sometimes on the opposite end of the fight as the U.S. and its coalition partners, things have the potential to escalate quickly.

Russia's military has also brought capabilities to the fight that many American troops haven't faced since the Cold War, including electronic warfare and air-defense systems.

The U.S. has about 2,000 troops in Syria. If they leave, which Trump announced they would do via a Twitter video in December, surprising military allies, Votel said it will create a void that Russia will quickly work to fill.

In his Twitter message, Trump said the fight against ISIS had been "won" and that "our boys, our young women, our men -- they're all coming back and they're coming back now."

Votel said during the hearing that the fight against the terror group is "far from over."

Trump has since reversed course on his decision to pull all U.S. troops from Syria, NBC News reported this week, telling members of Congress that he agreed 100 percent with keeping a military presence there.

Rep. Trent Kelly, a Mississippi Republican member of the House Armed Services Committee and brigadier general in the Army National Guard, hit back against the idea that Trump's decision to withdraw troops from Syria would be responsible for creating the void Russia would fill. That happened, he argued, during the Obama administration.

"Our failure to respond in Syria in 2013 left a void which the Russians quickly filled where they had not been before," Kelly said. "Because we had no action whatsoever for a long period of time -- even a delayed reaction after ... the government gassed their own people -- that is part of the reason that we have Russian influence in Syria now. Not just the tweets of recent days."

-- Gina Harkins can be reached at gina.harkins@military.com. Follow her on Twitter @ginaaharkins.