One of the world’s biggest cryptocurrency exchanges has moved to sue the North Korean regime and state-sponsored cybercriminals over a $1.5 billion heist carried out last year, seeking to recover funds stolen in the largest cryptocurrency theft in history.

In a press release Friday, the Dubai-based exchange Bybit said it filed a civil lawsuit in the U.S. District Court for the District of Columbia against the DPRK government, the Lazarus Group cybercrime syndicate and the Reconnaissance General Bureau (RGB), the North Korean military’s main spy agency.

The exchange added that it also secured a preliminary injunction freezing stolen assets linked