(CNN) In a blistering attack on Boeing, the Air Force's top acquisition official said the company has a "severe situation" with flawed inspections of its new KC-46 air refueling tanker aircraft, after trash and industrial tools were found in some planes after they were delivered to the Air Force.

Dr. Will Roper, assistant secretary of the Air Force for acquisition, technology and logistics, made clear his concerns after visiting Boeing's Everett Washington plant where the plane is assembled.

"I left concerned, and I also left thinking Boeing understands they have a severe situation that's going to take top level engagement from their company," Roper said.

After discovering the problem, the Air Force stopped accepting the new tankers from Boeing on February 20.

Roper visited the plant on Monday and, after getting a company promise for a new inspection plan, deliveries are resuming as upgraded inspections are completed. Six aircraft that had already been received were re-inspected by the Air Force.

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