North Korea, which has reportedly sent ground troops to join Russia’s war against Ukraine, has also sent fighter pilots capable of flying Russian warplanes, a report said Monday.

A government official in South Korea claimed that North Korea had sent fighter pilots to Vladivostok, a city in the Russian Far East, last month ahead of the first deployment of its ground forces on October 8, South Korean media TV Chosun reported.

This could be related to training on Russian fighter jets supplied to North Korea, the report said. But it could not rule out that Russia, which faced a shortage of pilots during the war between Russia and Ukraine, had asked for help from the North.

Russia would be the first overseas deployment for fighter pilots from the North since the Vietnam War. They also operated in Syria and Egypt during the 1973 Yom Kippur War.

Newsweek has contacted the North Korean embassy in China by email for comment.

Both Ukraine and South Korea have accused North Korea, ruled by Kim Jong Un, of sending troops to support Russian President Vladimir Putin’s war efforts. The Kremlin claimed that cooperation with the North “is not directed against third countries.”

On Monday, a North Korean representative to the United Nations for the first time refuted Kiev and Seoul’s accusations, saying their accusations were “baseless stereotypical rumors” and that Pyongyang has a legitimate and cooperative relationship with Moscow.

Seoul is considering sending intelligence personnel to Ukraine to monitor North Korean troops fighting the Russians, South Korea’s Yonhap News Agency reported Tuesday. The country is also considering supplying weapons to Kiev.

North Korea has more than 900 combat aircraft, the United States Defense Intelligence Agency said in a 2021 report. The country’s most capable combat aircraft were purchased from the Soviet Union, including Su-25 ground attack aircraft and MiG-29 fighter jets.

The Su-25 has been used extensively in Ukraine’s airspace, where several have been shot down.

Dutch open-source defense analysis website Oryx has visually confirmed that 114 Russian aircraft have been destroyed and 15 damaged since the start of the full-scale war in Ukraine in February 2022, including 34 Su-25 aircraft.

The U.S. intelligence report also alleged that due to fuel shortages and concerns about aging aircraft, Northern Air Force pilots were only in the air 15 to 25 hours per year, leaving them inadequately trained and unable to maintain combat readiness.

Meanwhile, the South’s air force said Tuesday that its commanders had met American counterparts at a meeting at Osan Air Base in Pyeongtaek, 60 kilometers (37 miles) south of Seoul. The security situation was assessed amid the North’s continued provocations and decision to send troops to Russia.