The Pentagon said Monday it believes that Russia is now trying to recruit Syrian fighters to bolster the Russian war effort in Ukraine.

The Wall Street Journal first reported the story Sunday, saying Russia is seeking Syrians who have taken part in urban combat and could help Russia take control of cities such as Ukraine's capital Kyiv.

"The accounts of the Russians seeking Syrian fighters, to augment their forces in Ukraine, we do believe there's truth to that," Pentagon spokesman John Kirby told reporters. "It's interesting that (Russian President Vladimir) Putin would have to rely on foreign fighters."

Kirby said he had no information on the numbers or the caliber of the Syrian fighters that the Russians are trying to sign up.

Russia has not commented on the reports.

It's not clear how long it might take such a group of Syrian fighters to reach Ukraine, how they would integrate with the Russian military, or how effective they might be in a country they are not familiar with.

Still, the Russian recruiting effort is the latest sign that Russia's invasion of Ukraine is not going as planned.

Some Russian forces have entered southern cities in Ukraine, but Russian efforts in the north — outside Kyiv and other key cities — have largely been stalled in recent days.

The Pentagon says Russia has now deployed "nearly 100 percent" of the combat forces that it had positioned near Ukraine's borders in advance of the war, which is now in its 12th day.

There are no signs at present that Russia is moving forces from other parts of Russia toward Ukraine, according to the Pentagon.

Russian leader Vladimir Putin sent the Russian military in 2015 to support Syrian President Bashar al-Assad in that country's civil war, and the Russians remain there to this day.

The Russian military in Syria consists mostly of air force units that have carried out airstrikes. They were involved in a devastating bombing campaign in the northern city of Aleppo in 2016 that flattened many neighborhoods and resulted in large numbers of civilian casualties.

Meanwhile, the Pentagon said the U.S. is sending an additional 500 troops on temporary assignments to NATO countries as part of the response to the Ukraine crisis. The American forces will be going to Greece, Germany, Poland and Romania.

With additional troops being rotated into the region on a temporary basis, the total U.S. force in Europe is now approximately 100,000, the Pentagon added.

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