Starting today, you can launch Amazon EC2 instances with encrypted Amazon Elastic Block Store (EBS) boot volumes in AWS GovCloud (US). This feature simplifies security compliance processes by now providing encryption for both EBS data and boot volumes using the AWS Key Management Service (KMS). It can also help simplify your auditing processes because you now have the ability to ensure all data on EBS is encrypted at rest and in transit. This feature is supported with all EBS volume types.
Source: Amazon Web Services News AWS GovCloud (US) now supports Amazon EBS encrypted boot volumes and AMI copy