The U.S. Coast Guard has suspended its search for the six people aboard an Ontario-based air ambulance that vanished over the Atlantic early Saturday morning.

Coast Guard crews called off the search at sunset on Sunday after roughly 66 hours of effort covering more than 4,400 square miles of ocean off Nantucket, Massachusetts. Debris confirmed to be from the aircraft, a Gulfstream G100 with tail number C-GRJP operating under the callsign Heartbeat 104, was found about 20 miles south of Nantucket.

The aircraft, operated by Hamilton-based Latitude Air Ambulance, was flying from Bermuda to Boston when contact was lost between 1:20 and 2:00 a.m. Saturday. Six people were aboard: four Canadian crew members, including two pilots and two medical staff, plus a Bermudian patient and a family escort. Their names have not been released.

Latitude Air Ambulance says it now presumes all six are dead. The company is working with the U.S. National Transportation Safety Board and Canada's Transportation Safety Board on the recovery and investigation.