Secretary of State John Kerry
Secretary of State John KerryThinkstock

Secretary of State John Kerry will send a letter to all members of Congress on Wednesday, in which he will stress Washington’s security commitments to Israel and the Gulf Arab states in light of the Iran nuclear deal, The Associated Press (AP) reported Tuesday.

State Department officials quoted by the news agency said 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, which will take place 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 to AP on condition of anonymity.

Kerry, who has been vocal in his criticism of opponents of the Iran deal, said recently he "profoundly disagrees" with the reasoning behind decisions by Democratic lawmakers to vote against the deal.

At the time, the Secretary of State said he respects the right of lawmakers to make their own decisions about the merits of the deal, but said rejection does not offer any alternative than a drumbeat to conflict.

Kerry has also warned that if the United States walks away from the deal, it would threaten ties with other world powers and could affect the dollar's position as the world's reserve currency.

The top diplomat has also been very critical of Prime Minister Binyamin Netanyahu’s opposition to the Iran deal. In July, he warned that Israel might be blamed if Congress blocks the accord with Iran, and that as a result Israel might “wind up being more isolated.”

That statement came hours after Kerry warned Israel that a unilateral strike on Iran's covert nuclear program would be a "huge mistake."