Seoul, Jun 24 (IANS): US Deputy Secretary of State Kurt Campbell expressed "strong" support for "any measures" taken by South Korea in response to the expanding illegal military cooperation between Russia and North Korea in phone talks with his South Korean counterpart on Monday, Seoul's foreign ministry said.

Campbell made the remark as he spoke by phone with First Vice Foreign Minister Kim Hong-kyun, as tensions have heightened after Moscow and Pyongyang signed a new partnership treaty that pledges mutual defence aid in the event that either is attacked, reports Yonhap news agency.

Campbell "expressed strong support for any measures taken by the South Korean side in response to the security threats posed by the illegal military cooperation between Russia and North Korea," Seoul's foreign ministry said in a release.

They also expressed "grave concern" over the deepening military ties between the two isolated states and "strongly condemned" them, the ministry said.

South Korea said it will reconsider its stance on the arms supply to Ukraine, indicating a possible policy shift to providing lethal aid to Kyiv.

National Security Adviser Chang Ho-jin said Sunday that South Korea will not be bound by anything concerning its assistance to Ukraine if Russia provides the North with precision weapons, seen as a warning to Moscow not to cross the line.

The two sides agreed to keep close tabs on any potential provocations by the North and maintain a thorough readiness based on strong extended deterrence, as they will continue close coordination over the issue, the ministry said.

The two sides also exchanged opinions on the outcome of the security dialogue South Korea had with China last week, the ministry added.