US President Donald Trump on Monday urged Boeing Co to fix and "rebrand" its troubled 737 MAX jetliner following two fatal crashes even as US regulators continued to work with the planemaker and airlines regarding the now-grounded aircraft.

The Federal Aviation Administration has been meeting with representatives from American Airlines Group Inc, United Airlines and Southwest Airlines Co over the next steps after more than 300 Boeing 737 MAXs were grounded worldwide.

FAA officials have also convened a joint review with aviation regulators from other countries, while federal prosecutors, the US Department of Transportation inspector general's office and a blue-ribbon panel are reviewing the plane's certification.

In an early-morning post on Twitter, Trump, who owned the Trump Shuttle airline from 1989 to 1992 and is an aviation enthusiast, weighed in with his own advice.

"What do I know about branding, maybe nothing (but I did become President!), but if I were Boeing, I would FIX the Boeing 737 MAX, add some additional great features, & REBRAND the plane with a new name. No product has suffered like this one. But again, what the hell do I know?" Trump tweeted.

The plane's grounding has also threatened the US summer travel season, with some airlines removing the 737 from their schedules through August and canceling a number of scheduled flights.