About EC2 Snapshots

An EC2 EBS Snapshot represents an EBS volume at a particular point in time. You can create a snapshot regardless of whether or not a volume is attached to an instance. When a snapshot is saved to S3, it receives a timestamp and a unique AWS ID (e.g. snap-9cea0df5). Snapshots consist of a series of data blocks that are incrementally saved to S3. Create clones of volumes from any snapshot. You cannot attach the same volume to multiple instances. Instead, you must first take a snapshot of the volume, then create a clone of the volume from the snapshot and specify the appropriate availability zone.

EBS volumes and snapshots are EC2 region-specific.  You cannot use a volume/snapshot that you created in EC2-US in a different region like EC2-EU.