U.S. President Donald Trump called Boeing Chief Executive Dennis Muilenburg this week to ask about the status of 737 MAX production, two people briefed on the matter confirmed.

The call on Sunday was brief and Muilenburg assured Trump that the planned production halt was temporary and that the company would not be laying off any workers. The production halt, set to begin in January, was announced by Boeing Monday after a board meeting.

Boeing and the White House declined to comment on the call, reported earlier by the New York Times.

Separately, S&P Global Ratings on Thursday downgraded Boeing's credit rating to "A-" from "A" and lowered the short-term rating to "A-2" from "A-1."

The change "reflects the uncertainty over when the 737 MAX will return to service, the risk to the supply chain from the planned production halt, and possible long-term impact to Boeing's competitive position."

U.S. officials have repeatedly said they are waiting for additional answers from Boeing and have at time faulted the quality of submissions from the planemaker since the plane was grounded in March after two fatal crashes killed 346 people.

"We've had conversations about the importance of making sure that we are looking at complete documentation and not piecemeal documentation," FAA Administrator Steve Dickson told Reuters in September. "It's really better to be very methodical and very detailed rather than try to rush a partially completed product and then say, 'We'll get back to you with the rest of it.'"

Boeing has repeatedly said it is working with regulators to safely return the plane to service and acknowledged last week it would not occur until 2020.

Dickson said last week there are nearly a dozen milestones that must be completed before the MAX returns to service. Approval is not likely until at least February and could be delayed until March, U.S. officials told Reuters last week.

American Airlines Group Inc and Southwest Airlines Co have canceled flights into April because of the grounding.