As many as 8,000 North Korean troops have been deployed to Russia's western front-line Kursk region and are expected to enter into combat "in the coming days," US Secretary of State Antony Blinken said Thursday, warning that they would become "legitimate" military targets.

Blinken made the remarks during a press conference after he, Defense Secretary Lloyd Austin, South Korean Foreign Minister Cho Tae-yul and Defense Minister Kim Yong-hyun held their "two-plus-two" meeting at the State Department in Washington.

The meeting underscored the two countries' close security coordination just a day after North Korea fired what appeared to be a new solid-fuel intercontinental ballistic missile (ICBM), ratcheting up tensions just days ahead of the US presidential election set for Tuesday.

"We now assess that there are some 10,000 North Korean soldiers in total in Russia, and the most recent information indicates that as many as 8,000 of those North Korean forces have been deployed to the Kursk Region," Blinken said.

"We've not yet seen these troops deploy into combat against Ukrainian forces, but we would expect that to happen in the coming days," he added.

The secretary pointed out that Russia has been training North Korean troops in artillery, unmanned aerial vehicles and basic infantry operations, including trench clearing, indicating that Moscow "fully" intends to use the soldiers in front line operations.

"Should these troops engage in combat or combat support operations against Ukraine, they would become legitimate military targets," he said.

Austin also warned against North Korean troops' potential entry into combat.

"We are consulting closely with our allies and partners in other countries in the region on these reckless developments and on our response," he said without elaboration.

During the press conference, Kim noted that North Korea has so far sent some 1,000 missiles and "millions of artillery rounds -- a figure close to 10 million" -- to Russia.

Blinken highlighted that a reason why Russia is turning to North Korean troops is that it is "desperate."

"Putin has been throwing more and more Russians into a meat grinder of his own making in Ukraine. Now he's turning to North Korean troops, and that is a clear sign of weakness," he said.

"Russia's been suffering some 1,200 casualties a day in the east, more than at any other time during the war, and with the deployment of these North Korean troops to Russia and now to the front lines, this is the first time in 100 years that Russia has invited foreign troops into its country."

Noteworthy was that both South Korean and US officials mentioned the shared goal of the denuclearization of the Korean Peninsula during the press conference, as questions had lingered over the absence of a reference to that goal in the joint communique of the allies' annual defense talks held on Wednesday.

"We reaffirmed the goal of North Korea's complete denuclearization," Cho said in his opening remarks. Kim also made a similar statement.

Blinken touched on the issue in response to a related question from a Korean reporter.

"Our policy remains what it has been and will remain, which is the complete denuclearization of the Korean Peninsula," he said.

As a mention of the denuclearization goal was absent in the joint communique, questions surfaced over whether there was a shift in policy focus to deterring North Korean threats rather than seeking the complete denuclearization of the Korean Peninsula.

Commenting on the North's weapons of mass destruction programs, Cho underscored that Seoul and Washington agreed to make "active" efforts to ensure that Pyongyang's nuclear weapons and missiles will become a "liability" rather than strategic assets.

Cho also said that the two governments agreed to hold the two-plus-two meeting of their top diplomats and defense chiefs on a regular basis to "expand and deepen the breadth and depth of the alliance."

Asked to comment on China's role regarding North Korean activities, the South Korean defense minister anticipated that though Beijing has been in a "wait-and-see" mode, it could play "some sort of role" at a time when the situation worsens and undermines its interests.

Regarding a question of when a North Korean nuclear attack scenario will be incorporated into combined military exercises between South Korea and the US, Kim said that it is expected to happen within the "earliest" timeframe.

During their annual talks at the Pentagon on Wednesday, Kim and Austin decided to include "realistic" scenarios, including a North Korean nuclear attack, in combined exercises, signaling the possibility that those scenarios will be included in the allies' wartime contingency plans.

In response to a question about the possibility of Russia's technological support for the North's latest ICBM test, Austin said the US is in an early assessment phase over the launch, and that it does not see any indication of Russian involvement yet.

"But again, let me emphasize how irresponsible this behavior is. And we call upon the DPRK to cease and desist," he said, referring to the North by its official name, the Democratic People's Republic of Korea.

Earlier in the day, Cho, Blinken and Japanese Foreign Minister Takeshi Iwaya held a phone call to condemn the North's ICBM launch. They issued a joint statement, calling the launch a "flagrant" violation of multiple U.N. Security Council resolutions.

"We strongly urge the DPRK to immediately cease its series of provocative and destabilizing actions that threaten peace and security on the Korean Peninsula and beyond," they said in the statement.

They also stressed that the three nations condemn "in the strongest terms" deepening military cooperation between the North and Russia, including continued arms transfers, as well as the deployment of North Korean troops to Russia.

"The United States reiterates that its commitments to the defense of the ROK and Japan are ironclad and backed by the full range of capabilities, including nuclear," it read. "The three countries will continue to strengthen our trilateral security cooperation to deter and respond to the DPRK's advancing nuclear and ballistic missile threats more effectively."

ROK stands for South Korea's official name, the Republic of Korea. (Yonhap)