In this Monday, Dec. 16, 2019, file photo, a Boeing worker walks in view of a 737 MAX jet in Renton, Wash.



Teams looking in the fuel tanks of brand new Boeing 737 Max planes for foreign object debris will expand their inspections, sources familiar with the checks told CNBC on Friday.

The expanded inspections are the result of teams finding debris in about two-thirds of the 737 Max models that have been checked, the sources told CNBC.

The news, first reported by Dow Jones on Friday, is the latest indication Boeing continues to wrestle with issues involving the Max.

The plane has been grounded by regulators around the world since March of last year following two crashes that killed 346 people.

Boeing released the following statement regarding the initial checks for foreign object debris, commonly referred to as FOD, in more than 400 new, but not yet delivered Max planes:

"We are taking steps to make sure we eliminate FOD from any and all aircraft. This is unacceptable and won't be tolerated on any Boeing aircraft when it's delivered to the customer."