Jan 6 (Reuters) - Alaska Airlines said it had halted flights by 18 Boeing MAX 9 airplanes pending potential additional maintenance work that U.S. regulators may require.

The airline had resumed flights on 18 of its 65 MAX 9 planes that had received in-depth inspections as part of heavy maintenance checks.

The entire Alaska MAX 9 fleet was voluntarily grounded early on Saturday after one of its planes had been forced to make an emergency landing.

Alaska Airlines said it was halting the use of MAX 9 planes after receiving an emergency directive from the Federal Aviation Administration and was "in touch with the FAA to determine what, if any, further work is required before these aircraft are returned to service." (Reporting by David Shepardson; Editing by William Mallard)