(COLORADO) — United States Northern Command recommended that search operations conclude as of Friday, Feb. 17, as search activities have been unable to recover any debris from airborne objects shot down on Feb. 10, and Feb. 12, according to a press release.

The U.S. military, federal agencies and Canadian partners conducted systematic searches of each area using airborne imagery and sensors, surface sensors and inspections, and subsurface scans. Despite these efforts, no debris was located, stated a press release sent by U.S. Northern Command and the North American Aerospace Defense Command (NORAD).

“The Secretary of Defense concurred with the recommendation,” said the press release.

U.S. Northern Command and NORAD said it worked closely with the Alaska National Guard, Federal Bureau of Investigation (FBI) and U.S. Indo-Pacific Command to position teams to expedite recovery in Deadhorse, Alaska.

Arctic conditions and sea ice instability were factors considered in the decision to conclude search operations. The press release stated air safety perimeters will be lifted after flight operations conclude on Friday.

U.S. Coast Guard District 9, the FBI, Canadian Coast Guard, and the Royal Canadian Mounted Police have not been able to identify debris after multiple days of surface searches and subsurface scans on Lake Huron, per U.S. Northern Command and NORAD. Air and maritime safety perimeters have been lifted.

Recovery operations concluded on Thursday, Feb. 16, off the coast of South Carolina, after U.S. Navy assets assigned to U.S. Northern Command located and retrieved debris from the high-altitude PRC surveillance balloon shot down on Saturday, Feb. 4, according to the press release.

Final pieces of debris are being transferred to the FBI Laboratory in Virginia for “counterintelligence exploitation, as has occurred with the previous surface and subsurface debris recovered.” U.S. Navy and U.S. Coast Guard vessels have departed the area. Air and maritime safety perimeters have been lifted.