Russian President Vladimir Putin and North Korean leader Kim Jong Un on Wednesday signed a new partnership that includes a vow of mutual aid if either country faces “aggression,” in a pact that came as both face escalating standoffs with the West.

Details of the deal were not immediately clear, but it could mark the strongest connection between Moscow and Pyongyang since the end of the Cold War. Both leaders described it as a major upgrade of their relations, covering security, trade, investment, and cultural and humanitarian ties.