The South Korean president on Monday called military ties between North Korea and Russia "illegal," vowing "thorough countermeasures" from Seoul.
"The recent international security situation and the illegal military cooperation between North Korea and Russia pose a significant threat to our national security," Yoon Suk Yeol told parliament in a budget speech read by Prime Minister Han Duck-soo.
"We will thoroughly review all possible scenarios to prepare countermeasures," Yoon added.
It was the first time in 11 years that a sitting president has not presented the budget in person to the parliament in South Korea, Seoul-based Yonhap News reported.
Yoon's comments came amid claims by Seoul, backed by the U.S. and NATO, that Pyongyang has dispatched thousands of troops to Russia.
While neither confirming nor refuting Seoul's claims, Pyongyang has pledged to support Moscow until victory is achieved in Ukraine, where the conflict has lasted nearly two years and nine months.
However, Yoon boasted of Seoul's trilateral security cooperation with Japan and the U.S. against Pyongyang.
In June, Russia and North Korea elevated ties and signed a pact that requires extending military aid in case of aggression by a third party.
On Saturday, South Korea and Canada called on North Korea to withdraw its troops from Russia and stop helping Moscow in its war against Ukraine.
On Sunday, Pyongyang released a White Paper calling Yoon's policies "disastrous," which has exposed South Korea to the "danger of a nuclear war."
"The more desperately Yoon tries to escalate the present crisis and get rid of the abyss of ruin, the deeper he will be sunken due to his thrice-cursed crimes," the paper warned.
