Boeing's crisis-hit 737 Max jetliner faces a new potential safety issue as debris has been found in the fuel tanks of several of the planes.
The head of Boeing's 737 programme has told employees that the discovery was "absolutely unacceptable".
A Boeing spokesman said the company did not see the issue further delaying the jet's return to service.
It comes as the 737 Max remains grounded after two fatal crashes.
The US plane maker said it discovered so-called "Foreign Object Debris" left inside the wing fuel tanks of several undelivered 737 Maxs.
