It's time for the United States to hold Iran accountable.

Iran's top leader on Tuesday called for vigilance in ensuring that world powers meet their commitments under a newly implemented nuclear deal while expressing "pessimism" about U.S. intentions, state media reported.

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 said 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 on Tuesday. Khamenei said Iran has paid heavy prices for concluding the deal.

Read the full story from the Associated Press.