(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.
"We are doing more stringent inspections so we feel confident before we accept any plane from Boeing," Air Force spokeswoman Ann Stefanek told CNN.
While the discovery of trash and tools in the planes is not a result of design flaw, or a specific safety concern, Air Force officials privately told CNN they were aware that the timing of the problem is exceptionally sensitive for Boeing after the grounding of its 737 Max jet.
Roper emphasized to reporters that while the issue of the material and objects -- known as Foreign Object Debris, or FOD -- being left inside an aircraft as it comes off the production line is not a design or safety risk, it is a matter of great concern to the military.
"FOD is really about every person, everyone in the workforce, following those procedures and bringing a culture of discipline for safety," Roper said.
"Culture is something that I'm not going to believe because we have a good month, or a good two months, that the culture is back. I'm going to believe it when I see month after month for a long time that yes, those practices are now things that aren't just being done because they have to be done, they are being done because the workforce says, 'This is a product we deliver to the Air Force,'" he added.
Boeing will now have to conduct spot inspections on the aircraft during production, including specific areas of the planes that may be sealed as part of the production processes.
"I certainly think they are going to have to have a good team," to carry out the new inspection program, Roper said.
The KC-46 plays a critical role in the refueling of military aircraft around the world.
The issue was first reported by various defense industry publications.