The Pentagon confirmed Tuesday that a "small number" of North Korean troops are in Russia’s Kursk region near the Ukrainian border, adding that a couple of thousand more soldiers are expected to arrive at any time.

Last week, White House National Security communications director John Kirby confirmed that between early to mid-October, North Korea moved at least 3,000 troops into eastern Russia.

Now, the Pentagon says about 10,000 North Korean troops have been sent to Russia, and they are preparing to be sent to the battle lines alongside Russian troops in their fight against Ukraine.

"We believe that the DPRK [Democratic People's Republic of Korea] has sent approximately 10,000 soldiers in total to train in eastern Russia, and that these troops will probably augment Russian forces near Ukraine over the next several weeks," Pentagon press secretary Maj. Gen. Pat Ryder told reporters during a news briefing Tuesday. "A portion of those soldiers have already moved closer to Ukraine towards Russia's Kursk Oblast, near the border with Ukraine."

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Ryder said the troops are in addition to a couple of thousand others already in the Kursk region, adding the Department of Defense (DoD) is concerned that Russia intends to use the soldiers in combat or to support combat operations against Ukraine.

"Indications that there's already a small number [of North Korean troops] that are actually in the Kursk Oblast, with a couple of thousand more that are either almost there, or due to arrive imminently," he said.

The Pentagon could not confirm whether the North Korean soldiers were in fact inside Ukraine, yet.

"Initial indications are that these troops will be employed in some type of infantry role," Ryder reiterated. "But again, what that could be remains to be seen. So, we're going to continue to monitor closely."

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Like the DoD, President Biden expressed concerns about North Korean soldiers preparing for battle against Ukraine in Russia.

After speaking about infrastructure in Baltimore on Tuesday, a reporter asked Biden if he was worried about North Korean troops in Russia.

"I am concerned about it, yes," he said.

Biden was then asked if Ukrainians should strike back.

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"If they cross into Ukraine, yes," Biden said.

Intelligence officials in both South Korea and Ukraine had previously stated that North Korean troops were being transferred to Russia.

"What exactly are they doing? Left to be seen. These are things that we need to sort out," Defense Secretary Lloyd Austin has said.

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Russia and North Korea have denied the troop movements.

South Korean National Intelligence Service Director Cho Tae-yong told lawmakers that North Korea plans to deploy 10,000 troops to Russia by December, a number that lines up with claims from Ukrainian intelligence.

South Korea said last week that it may start sending weapons to Ukraine in reaction to the deployment. Officials said their response would come in phases linked to the depth of cooperation between Russia and North Korea.

North Korea and Russia, locked in separate confrontations with the West, have sharply boosted their cooperation in the past two years. The U.S., South Korea and their partners have accused North Korea of supplying artillery shells, missiles and other conventional arms to Russia to help fuel its war against Ukraine in return for economic and military assistance. 

In June, Kim and Russian President Vladimir Putin signed a pact stipulating mutual military assistance if either country is attacked.

Fox News Digital’s Anders Hagstrom and Greg Norman, as well as The Associated Press contributed to this report.