This article was originally published by Radio Free Asia and is reprinted with permission.

Russian President Vladimir Putin warned South Korea that sending  weapons to Ukraine would be a “very big mistake” after South Korea said it would consider doing so in response to a pact between Russia and North Korea to come to each other’s aid if attacked.

U.S. ally South Korea announced on Thursday it would reconsider its stance on arms to Ukraine in response to North Korea and Russia signing a treaty the previous day that  includes a mutual pledge to provide immediate military assistance if either is attacked.

“As for the supply of lethal weapons to the combat zone in Ukraine, it would be a very big mistake. I hope it will not happen. If it does, then we too will then make the respective decisions, which South Korea’s current leadership is unlikely to be pleased with,” Putin told a press conference on Thursday during a visit to Vietnam, Russia’s Sputnik news agency reported.

South Korea’s assistance to Ukraine has included first-aid kits, medicine, portable mine detectors and protective gear but it has not supplied weapons in line with a policy of not providing lethal aid to countries engaged in conflict.

During Putin’s first visit to North Korea in 24 years, he and leader Kim Jong Un, agreed to offer military assistance “without delay” if either is attacked under a new partnership treaty signed after their summit on Wednesday.

South Korea’s National Security Adviser Chang Ho-jin condemned both countries on Thursday, saying that Seoul would have to think again about  supplying arms.

“We plan to reconsider the issue of arms support to Ukraine,” Chang said in a press briefing at the presidential office.

He added that any cooperation that directly or indirectly aided North Korea’s military enhancement was a violation of U.N. Security Council resolutions and would be subject to international scrutiny and sanctions.

“The government expresses grave concern and condemns the signing of the comprehensive strategic partnership agreement between North Korea and Russia, which aims to strengthen mutual military and economic cooperation,” Chang said. 

John Kirby, the spokesperson for U.S. President Joe Biden’s National Security Council, said the announcement by Russia and North Korea of their pact to come to each other’s help if attacked was “no surprise” but it boded poorly for the people of Ukraine and the Korean peninsula.

“Our view is that this agreement is also a sign of Russia’s desperation,” Kirby added. 

“I mean, they’re reaching out to North Korea for missiles, and they’re getting drones from Iran. They don’t have a lot of friends in the world.”

North Korea has supplied Russia with large amounts of weapons for its war in Ukraine, in particular artillery rounds and ballistic missiles, the United States has said, though both Russia and North Korea deny that.