WASHINGTON- U.S. Secretary of State Mike Pompeo said on Monday the United States would impose the "strongest sanctions in history" against the Iranian leadership, after Washington pulled out of the 2015 nuclear deal.

Pompeo laid out 12 demands for Iran and said relief from sanctions would only come when Washington had seen tangible shifts in Iran's policies.

(Reporting by Lesley Wroughton Writing by Yara Bayoumy; Editing by Bernadette Baum) ((yara.bayoumy@thomsonreuters.com; tel: +1202 779 1681; Twitter: @yarabayoumy; Reuters Messaging: yara.bayoumy.thomsonreuters.com@reuters.net))