WASHINGTON, June 2 (CGTN) -- The U.S. Federal Aviation Administration on Sunday disclosed a new problem involving Boeing Co's grounded 737 MAX, saying that more than 300 of that troubled plane model and the prior generation 737 may contain improperly manufactured parts and that the agency will require these parts to be quickly replaced.

The FAA said up to 148 pieces of the part known as a leading-edge slat track that were manufactured by a Boeing supplier are affected, covering 179 MAX and 133 NG aircraft worldwide.

Slats are movable panels that extend along the wing's front during takeoffs and landings to provide additional lift. The tracks guide the slats and are built into the wing.

The 737 MAX, Chicago-based Boeing's best-selling jet, was grounded globally in March following a fatal Ethiopian Airlines crash after a similar Lion Air disaster in Indonesia in October last year. The two crashes together killed 346 people. Boeing has yet to submit a software upgrade to the FAA as it works to get approval to end the grounding of the 737 MAX.

In a statement issued after the FAA announcement, Boeing said it has not been informed of any in-service issues related to this batch of slat tracks. Boeing, the world's largest planemaker, said it has identified 20 737 MAX airplanes most likely to have the faulty parts and that airlines will check an additional 159 MAXs for these parts.

Boeing said it has identified 21 737 NGs most likely to have the suspect parts and is advising airlines to check an additional 112 NGs. The NG is the third-generation 737 that the company began building in 1997.

The affected parts "may be susceptible to premature failure or cracks resulting from the improper manufacturing process," the FAA said.

The FAA said a complete failure of a leading edge slat track would not result in the loss of the aircraft, but a failed part could cause aircraft damage in flight.

The FAA said it will issue an Airworthiness Directive to require Boeing's service actions to identify and remove the parts from service. It said operators will be required to perform this action within 10 days but can continue to fly the planes during the 10-day period before the parts are removed.