SEOUL, South Korea (AP) -- South Korea's president on Thursday raised the possibility of supplying Ukraine with weapons while stressing that his government "won't sit idle" as North Korea allegedly sends troops to support Russia's aggression toward its neighbor.

South Korean President Yoon Suk Yeol spoke to reporters after a meeting with Polish President Andrzej Duda that came a day after U.S. and South Korean officials said they believe around 3,000 North Korean troops have been deployed to Russia and are training at several locations. South Korea's spy agency told lawmakers that North Korea likely aims to send a total of 10,000 troops to Russia by the end of the year.

Yoon's meeting with Duda was focused on expanding defense cooperation between the countries amid the ongoing conflict. Poland has signed a series of arms deals with South Korea in the last two years to acquire tanks, howitzers and missile launchers in an effort to bolster its military capabilities following Russia's invasion of Ukraine.

Both Moscow and Pyongyang have denied the presence of North Korean troops.

Yoon said South Korea will work with allies and partners to prepare countermeasures that could be rolled out in stages depending on the degree of military cooperation between Pyongyang and Moscow.

Seoul's steps could potentially include sending weapons to Ukraine, which would mark a departure from a long-standing policy of not supplying weapons to countries actively engaged in conflict, Yoon said. He said North Korea's alleged troop deployment to Russia is a "provocation that threatens global security beyond just the Korean Peninsula and Europe."

"If North Korea dispatches special forces to the Ukraine war as part of Russia-North Korea cooperation, we will support Ukraine in stages and also review and implement measures necessary for security on the Korean Peninsula," Yoon said during a joint press conference with Duda.

"While we have maintained our principle of not directly supplying lethal weapons, we can also review our stance more flexibly, depending on the level of North Korean military activities," Yoon said.

Yoon's comments aligned with what a senior presidential official told reporters on condition of anonymity earlier this week. That official said South Korea is considering various diplomatic, economic and military options, including supplying Ukraine with both defensive and offensive weapons systems.

South Korea, a growing arms exporter, has provided humanitarian aid and other non-lethal support to Ukraine and joined U.S.-led economic sanctions against Moscow. It has so far resisted calls by Kyiv and NATO to directly supply Ukraine with weapons.

During their summit, Yoon and Duda agreed to "actively support" additional deliveries of South Korean military equipment to Poland, including a new deal for Korean K-2 tanks the governments hope to finalize within this year, Yoon's office said.

Tensions on the Korean Peninsula have worsened since 2022 after North Korean leader Kim Jong Un used Russia's invasion of Ukraine as a distraction to accelerate the growth of his nuclear weapons and missile program.

Seoul also worries as experts say the North may seek major technology transfers in return for sending troops, including Russian know-how on intercontinental ballistic missiles and submarines that would advance the threat posed by Kim's nuclear arsenal.

Experts say it's unclear how effective the North Korean soldiers would be in combat, considering their lack of active battlefield experience, outdated conventional weaponry and training experience with Russian forces. Kim may see the troop dispatch as a crucial opportunity to expose his soldiers to modern warfare and technologies, said Hong Min, an analyst at Seoul's Korea Institute for National Unification.

During a parliamentary hearing, South Korean Defense Minister Kim Yong Hyun said that North Korean troops would likely become "cannon fodder" when deployed in combat in Ukraine and denounced Pyongyang's leadership for "selling away its troops to an illegal invasion."

"Troop deployment is just a phrase, and it would be more appropriate to call them as mercenaries," he said. "The North Koreans are disguising themselves in Russian uniforms and operating under Russian control with no operational autonomy, just simply following orders."