WASHINGTON (Reuters) – U.S. President Donald Trump will strike a blow against the 2015 Iran nuclear agreement in defiance of international support for it on Friday, choosing not to certify that Tehran is complying with the deal in a major reversal of U.S. policy.

Trump will make the announcement in a speech at 12:45 p.m. EDT (1645 GMT) that will detail a more confrontational approach to Iran over its nuclear and ballistic missile programs and its financial and military support for extremist groups in the Middle East, U.s. Secretary of State Rex Tillerson told reporters.

Trump will also give the U.S. Treasury Department broad authority to impose economic sanctions against people and entities in the Iranian military, the Iran Revolutionary Guard, in response to what Washington calls its efforts to destabilize and undermine its opponents in the Middle East.

Trump’s decision to decertify the nuclear deal will not withdraw the United States from the agreement, which was negotiated by the United States and other world powers during the administration of former President Barack Obama.