Iran’s top leader has called for vigilance in insuring that world powers meet their commitments under a newly implemented nuclear deal while expressing “pessimism” about U.S. intentions.

In his first public remarks since international sanctions were lifted following a U.N. report that Iran had fully complied in scaling back its nuclear program, Ayatollah Ali Khamenei says Tehran should “exercise care the other party implements its commitments.”

He added that “expressions by some U.S. politicians in recent days are matter of pessimism,” without elaborating.

The remarks, his first since the deal was implemented over the weekend, came in a letter to President Hassan Rouhani published by state media Tuesday.

Khamenei, the country’s top decision maker, has praised Iran’s negotiators while continuing to express deep mistrust of the United States.

(AP)