WASHINGTON (AP) — Secretary of State John Kerry will send a letter to all members of Congress on Wednesday outlining U.S. security commitments to Israel and the Gulf Arab states in light of the Iran nuclear deal.

State Department officials said Tuesday the letter would be sent shortly before Kerry delivers what is being billed as a major policy speech on the Iran agreement in Philadelphia. The officials said the speech, a week before Congress returns to work, will focus on how the deal makes the U.S. and its allies safer.

Kerry will also attack what the officials said is a "mythology" of false claims about what the deal will do. The officials spoke on condition of anonymity because they were not authorized to preview the speech by name.