WASHINGTON, Nov 23 (Reuters) - President Barack Obama said on Saturday that a deal between Iran and six major powers was an important first step toward a comprehensive solution to Iran's nuclear program.

Obama, in a late-night appearance at the White House, said that if Iran did not meet its commitments during a six-month period, the United States would turn off sanctions relief and "ratchet up the pressure."

Obama said Iran could not use its next-generation centrifuges under the deal and that the substantial limitations under the agreement "cut off Iran's most likely paths to a bomb."

With Senate Democratic leader Harry Reid warning that the Senate will seek additional sanctions on Iran, Obama said his administration would consult closely with Congress, but "now is not the time to move forward on new sanctions." (Reporting by Steve Holland; Editing by Peter Cooney)