March 15 (Reuters) - U.S. energy firms this week added oil and natural gas rigs for the third time in four weeks, energy services firm Baker Hughes said in its closely followed report on Friday.

The oil and gas rig count, an early indicator of future output, rose by seven to 629 in the week to March 15.

(Reporting by Scott DiSavino in New York and Anjana Anil in Bengaluru Editing by Marguerita Choy)