A federal agency says crew members on two Coast Guard boats involved in separate collisions last December were using cell phones or similar wireless devices.

The National Transportation Safety Board stressed Wednesday it has not determined the causes of the collisions in San Diego Bay and Charleston, S.C. The agency says crew members were using the devices for texting or conversations unrelated to vessel operations.

The NTSB did not say how many crew members were using wireless devices or what their roles were in vessel operations.

The agency is recommending the Coast Guard develop a policy on use of the devices.

In San Diego, a Coast Guard boat collided with another boat, killing a child and injuring four people. In South Carolina, a collision with a small passenger vessel injured six.