Russia should not make a mistake that could hurt its relations with South Korea in an “irreversible” way, a Seoul official warned on Thursday, in a tit-for-tat exchange of words after Moscow warned against Seoul hinting at potential arms support to Ukraine.

The comment from Seoul’s Foreign Ministry came a day after Maria Zakharova, a spokeswoman at the Russian Foreign Ministry, warned South Korea not to take rash steps that could bring about an irreversible outcome for the bilateral relations, Yonhap news agency reported.

Zakharova’s comments came in response to the remarks by South Korea’s National Security Adviser Chang Ho-jin that South Korea could consider supplying weapons to Kiev, depending on Moscow’s actions in the follow-up to the treaty it signed with North Korea on pledging mutual defence.

“We warn that Russia should not make a mistake that could lead to irreversible consequences in South Korea-Russia relations,” Ministry spokesperson Lim Soo-suk said in a regular press briefing.

“Additionally, we hope that the Russian side will move away from relying on North Korea and act appropriately as a permanent member of the UN Security Council,” Lim added.

Tensions have heightened after Russian President Vladimir Putin and North Korean leader Kim Jong-un declared an upgrade of their countries’ relationship after talks in Pyongyang last week.

The new treaty commits them to providing mutual military assistance in case either of them is put under armed attack.

South Korea has expressed grave concerns over the growing military cooperation between Russia and North Korea in violation of UN resolutions, urging Moscow to act responsibly and cut off such military ties with Pyongyang.

Seoul’s Foreign Ministry said South Korean Ambassador to Russia Lee Do-hoon had a meeting with Russian Deputy Foreign Minister Andrey Rudenko in Moscow on Wednesday (local time) and heard Moscow’s position on the new partnership treaty with North Korea.

In the meeting, Lee stressed that any cooperation that would help North Korea’s arms buildup poses serious threats to security in the region, and called for Russia’s clear explanation of its actions.

Russia voiced regrets over South Korea’s reaction to Putin’s visit to Pyongyang, reiterating that its cooperation with North Korea is not directed at Seoul and the treaty is defensive, according to Seoul’s Foreign Ministry.