WASHINGTON (Reuters) - Congressman Ed Markey said on Thursday that Royal Dutch Shell may have moved the Kulluck oil rig that ran aground off Alaska to avoid $6 million in taxes, disputing claims by the company that it moved the rig because of weather forecasts.

Markey, in a letter sent to Shell President Marvin Odum on Wednesday, said the decision to move the rig "may have been driven, in part, by a desire to avoid ... tax liability on the rig."

Markey's office said the congressman received information about Shell and taxes from the Alaska revenue department.

(Reporting by Timothy Gardner; editing by John Wallace)