Lockheed Martin Corp said its Chief Executive Marillyn Hewson gave President-elect Donald Trump a personal commitment to bring down the price of its F-35 fighter jet, after he heaped pressure on the aerospace company over the cost.

Lockheed's shares fell on Friday after Trump's message on Twitter, and after he earlier tweeted that he had asked rival Boeing Co. to "price-out" an older aircraft as an alternative.

LM CEO just had a good conversation with @RealDonaldTrump… she personally committed to drive down the cost of the F-35! pic.twitter.com/K2aK7pW07f — Lockheed Martin (@LockheedMartin) December 23, 2016

Hewson said in a statement tweeted by Lockheed that the company would "aggressively" drive down the cost of the F-35, which brought in about 20 percent of Lockheed's sales last year.

Trump's transition team did not immediately respond to requests for comment.

Lockheed shares ended down nearly 1.3 percent in Friday trading on the New York Stock Exchange.