Nov 25 (Reuters) - The U.S. Federal Aviation Administration (FAA) is set to direct airlines to avoid flying Boeing Co 787 Dreamliners and 747-8 jumbo jets with General Electric Co engines near thunderstorms after some planes experienced ice buildup in their engines.

The U.S. regulator said it would issue an airworthiness directive (AD) this week for the airplanes powered by GE's GEnx engines.

"The AD is an interim action to make sure pilots avoid icing conditions that could affect engine power and possibly damage the engine," said FAA.

The FAA also said it has been working closely with Boeing and GE to monitor and understand these events as the companies develop a permanent solution.

The 787 can be powered by either GEnx engines or rival Trent 1000 engines made by Rolls-Royce Plc, while the 747-8 is powered exclusively by the GE engine model.

Boeing advised airlines on Friday about a risk of engine icing problems on 747-8 and 787 Dreamliner planes with GE engines, urging 15 carriers to avoid flying them near high-altitude thunderstorms.

Airlines affected by the warning included Japan Airlines , Lufthansa, United Airlines, a unit of United Continental Holdings and Cathay Pacific Airlines . The warning even led Japan Airlines to pull 787 Dreamliners from two international routes.

Boeing spokesman Marc Birtel said the company has already alerted its customers who operate some GE-powered engines on 747-8 and 787 models.

"To reduce chances of ice crystal conditions, Boeing recommends that operators fly at least 50 nautical miles from thunderstorms that may contain ice crystals," said Birtel.

So far, Boeing has delivered 57 747-8s and 58 787s with GEnx engines, Birtel said.