North Korea said Tuesday its top diplomat is visiting Russia, in another sign of their deepening relations as rival South Korea and Western nations say the North has sent thousands of troops to support Russia's war in Ukraine.

North Korea's official Korean Central News Agency said a delegation led by Foreign Minister Choe Son Hui departed for Russia on Monday, but didn't specify the purpose of the visit. In a closed-door hearing at South Korea's parliament, the South's spy agency said Choe may be involved in high-level discussions on sending additional troops to Russia and negotiating what the North would get in return, according to Lee Seong-kweun, a lawmaker who attended the meeting.