Photo/Illutration Russia’s President Vladimir Putin and North Korean leader Kim Jong Un attend a state reception in Pyongyang on June 19. (Pool via REUTERS)

SEOUL--North Korea's foreign minister, Choe Son Hui, is on her way to Moscow, state media KCNA and Russian officials said on Tuesday, for her second trip to Russia in six weeks amid rising concerns about Pyongyang's involvement in Moscow's war in Ukraine.

KCNA said a delegation led by Choe left on Monday for an official visit to Russia, without elaborating.

Russia's ambassador to Pyongyang, Alexander Matsegora, saw off Choe at the airport, the Russian embassy said in a statement posted on the embassy's Vkontakte social media page.

"The visit of the head of the DPRK Foreign Ministry to the Russian Federation is taking place within the framework of a strategic dialogue - following an agreement to enhance ties reached by the leaders of our countries during the June 2024 summit," the statement said.

DPRK stands for North Korea's official name, the Democratic People's Republic of Korea.

During a televised cabinet meeting, South Korean President Yoon Suk Yeol said "illegal" military cooperation between Russia and North Korea posed a serious threat to the international community.

"I want everyone to be on alert about risk management," Yoon told the meeting.

Choe's visit comes as NATO joined Seoul, Washington and Kyiv in confirming Pyongyang's dispatch of troops to Russia, saying that North Korean military units had been deployed to Russia's Kursk region on the border with Ukraine.

The Pentagon said on Monday that Washington would not impose new limits on Kyiv's use of American weapons if North Korea entered Moscow's war against Kyiv. It also said that North Korea had sent 10,000 troops to eastern Russia for training, up from its estimate of 3,000 on Wednesday.

U.S. President Joe Biden called the situation "very dangerous".

NATO Secretary-General Mark Rutte, after a meeting on Monday with a South Korean delegation, said the deepening military ties between Moscow and Pyongyang posed a threat to both Indo-Pacific and Euro-Atlantic security.

South Korea's president, in a phone call with European Commission President Ursula von der Leyen, said the deployment of North Korean troops to the front lines of the war in Ukraine may come sooner than expected.

Since the meeting of North Korean leader Kim Jong Un and President Vladimir Putin in Russia's Far East last year, North Korea and Russia have upgraded their military ties. They met again in June this year to sign a comprehensive strategic partnership that includes a mutual defence pact.