SEOUL - South Korea's foreign minister Cho Tae-yul and U.S. Secretary of State Antony Blinken condemned the new treaty between Russia and North Korea as a serious threat to regional peace and stability, Seoul's foreign ministry said in a statement on Friday.

The two in a phone call on Thursday also discussed ways to respond to the pact, and agreed to closely monitor the situation, the foreign ministry said.

Blinken said the United States supports South Korea's responses to the agreement, in which Moscow and Pyongyang said each country would provide immediate military assistance if either faces armed aggression.

Cho said any cooperation to help strengthen North Korea's military capabilities is a clear violation of the U.N. Security Council resolutions, according to the statement.

The United States will consider various ways to respond to the threat to international peace and stability from Russia and North Korea, Blinken was quoted as saying by the ministry.

South Korean National Security Adviser Chang Ho-jin said on Thursday that Seoul will review the possibility of supplying weapons to Ukraine in response to the landmark pact.

  - Reuters