Talks on the Iran nuclear deal are about to get underway in Vienna amid growing questions about the U.S. commitment to the plan.

President Donald Trump has vowed to walk away from the 2015 agreement in mid-May unless what the president calls fatal flaws are addressed. This week's firing of U.S. Secretary of State Rex Tillerson and the choice of Iran hard-liner Mike Pompeo to replace him have fueled speculation Washington will pull out.

An indication of American thinking could come Friday, when the U.S., Britain, China, France, Germany, Russia, the European Union and Iran gather for a periodic meeting of the so-called Joint Comprehensive Plan of Action Joint Commission, or JCPOA, in Vienna.

State Department policy planning chief Brian Hook is leading the U.S. delegation.