Russian President Vladimir Putin and North Korean leader Kim Jong Un signed an agreement Wednesday that pledges mutual aid if either country faces “aggression,” a strategic pact that comes 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, cultural and humanitarian ties, AP reported. 

The summit came as Putin visited North Korea for the first time in 24 years and the U.S. and its allies expressed growing concerns over a possible arms arrangement in which Pyongyang provides Moscow with munitions for its war in Ukraine, in exchange for economic assistance and technology transfers.