US Defense Secretary Lloyd Austin has addressed reports that North Korea is preparing to enter the war in Ukraine with troops.

“If they are co-belligerents and intend to participate in this war on behalf of Russia, that is a very, very serious matter,” Austin said.

Austin returned from his fourth visit to Kiev, where he announced a $400 million package of U.S. weapons for Ukraine.

White House national security spokesman John Kirby said Washington believes at least 3,000 North Korean troops arrived by sea this month in Vladivostok, Russia’s largest Pacific port.

“These soldiers then traveled on to several Russian military training areas in eastern Russia where they are currently undergoing training,” Kirby said Wednesday. “We do not yet know whether these soldiers will go into combat alongside the Russian military, but that is certainly a highly worrying probability.”

He added that if they were used to fight Ukraine, they would be “fair game.”

North Korea is also accused of exporting ballistic missiles and artillery shells that have already detonated on Ukrainian soil.

Ukrainian military intelligence chief Kyrylo Budanov told The War Zone, a US media outlet, that 11,000 North Korean infantrymen were being trained in eastern Russia and would be sent to Ukraine.

“They will be ready on November 1,” he said, adding that the first group of 2,600 would be sent to fight a Ukrainian counter-invasion in Kursk.

North Korean soldiers would use Russian weapons and ammunition, he said.

This figure was close to the figure reported by South Korea’s National Intelligence Service (NIS) on October 18. Yonhap News Agency said the NIS learned that Pyongyang recently decided to send four brigades with a strength of 12,000 soldiers to Ukraine.

Ukrainian President Volodymyr Zelensky also mentioned this number in his evening speech on Tuesday: “We have information that two units of military personnel from North Korea are being trained – possibly even two brigades with 6,000 men each.”

A week earlier, Zelensky told the Verkhovna Rada – the parliament in Kiev – that in addition to fighting, North Koreans would also replace Russian factory workers drafted to fight.

“The coalition of criminals with Putin’s state now includes North Korea,” he said.

The NIS said it monitored the first group of 1,500 soldiers brought to Vladivostok aboard four landing ships between October 8 and 13.

It said they were stationed at Russian military bases in the Russian port and in Ussuriysk, Khabarovsk and Blagoveshchensk in the north. They reportedly underwent training in Russian weapons and unmanned aerial vehicles.

Russia may be trying to cover up North Korea’s involvement with troops.

According to the NIS, the North Koreans were issued fake ID cards of the Republics of Yakutia and Buryatia “that looked similar to the North Koreans. It appears that they disguised themselves as Russian soldiers to hide that they were deployed on the battlefield.”

The NIS also estimated that North Korea had shipped 13,000 containers worth of artillery shells, anti-tank missiles and missiles. Both Ukrainian and U.S. defense intelligence have confirmed North Korean missile debris in Ukraine.

South Korea has indicated in the past that it might move to actively assist Ukraine with offensive weapons if North Korea were drawn into the war on Russia’s side.

On Monday, the Russian ambassador in Seoul tried to assure that Russian-North Korean cooperation “is not directed against the security interests of the Republic of Korea.”

If confirmed, the presence of North Koreans as fighters would suggest that Russia is not as well-staffed as it claims. Russia fights this war with volunteers and contract soldiers, often from former Soviet republics, and avoids using regular Russian conscripts.

Last week, Russian Security Council Deputy Chairman Dmitry Medvedev was quoted by state news agency TASS as saying the armed forces’ staffing plan for the year was 78 percent fulfilled.

“Overall, this rate is quite good,” said Medvedev.

But the numbers Russia needs to maintain the pace of its offensive operations are staggering.

For example, Ukraine suffered more than 1,300 Russian casualties per day last week and more than 600,000 Russian casualties for the entire war.

Al Jazeera is unable to verify these claims, but Medvedev said the Russian military signed up 190,000 contract fighters in the first half of the year alone.

Russia also lost a significant amount of equipment.

Ukraine’s Defense Ministry said Russia had lost at least 9,000 tanks, 18,000 armored fighting vehicles and 19,500 artillery systems as of mid-October.

Oryx, an independent open-source intelligence platform, has confirmed the loss of 3,500 individual tanks and more than 7,300 armored vehicles of various types.

Lloyd Austin estimated that the war has cost Russia over $200 billion so far.

Ukrainian National Guard spokesman Ruslan Muzychuk said Russian forces had increased the use of armored vehicles and tanks in recent days to take advantage of unseasonably dry weather ahead of the onset of winter.

Ukraine has recorded a high number of daily attacks in the eastern Donetsk region over the past week, with Russian forces particularly focused on Kurakhove and Pokrovsk.

These are towns west of Avdiivka that Russian forces captured in February, pressing their advantage as Ukrainian forces struggled to establish a new defensive line. Russian forces have formed a salient 40 km (25 miles) west of Avdiivka in recent months.

The Institute for the Study of War, a Washington-based think tank, said it had “observed three battalion-sized mechanized attacks in western Donetsk Oblast in the last week alone – a notable increase in pace given that ISW only reports on Russian forces “Conducted four battalion-sized mechanized attacks in eastern Ukraine from late July to early October 2024.”

Ukraine responded with a strong defense, meaning no new cities fell victim to Russian forces last week. In keeping with its policy this year, it has sought to expand the war into Russian territory with deep strikes.

The security service and military intelligence said their drones on Sunday attacked the Sverdlov weapons factory in the Nizhny Novgorod town of Dzerzhinsk, 900 kilometers (560 miles) from Ukraine.

According to Western intelligence services, it is one of Russia’s largest ammunition factories, producing explosives, artillery shells, glide bombs and anti-aircraft and anti-tank missiles.

On the same day, Ukrainian drones hit the Lipetsk-2 airbase, triggering secondary explosions.

On Friday evening, Ukraine attacked the Kremniy-El plant in Bryansk.

The head of the Ukrainian Center for Combating Disinformation, Andriy Kovalenko, said it is one of Russia’s largest microelectronics plants, producing chips and circuits for Iskander missiles, Pantsir air defense systems, drones, radars and electronic warfare systems.

This was the second major Ukrainian drone attack on Russian assets in ten days. On October 9 and 10, Ukraine attacked the oil depot in Feodosia in occupied Crimea, a Shahed drone camp in Yeysk and the Khanskaya airfield in Adygea.

Russian President Vladimir Putin was on the diplomatic offensive Tuesday and Wednesday, hosting 36 world leaders in Kazan in southwest Russia. His high-level scheduled meetings included South African President Cyril Ramaphosa, Chinese President Xi Jinping, Indian Prime Minister Narendra Modi and Egyptian President Abdel Fattah el-Sisi.

Putin called Sino-Russian relations “a model of how relations between states should be built in the modern world.”