An Iranian military official said Iran conducted its third ballistic missile test-firing since the country’s landmark nuclear deal went into effect in January, but a few hours later Iran’s defense minister countered the report.

The semiofficial Tasnim News Agency reported earlier Monday that the country fired a missile with a range of 2,000 kilometers (1,243 miles) two weeks ago, citing Brig. Gen. Ali Abdollahi. The missile was precision-guided and could accurately strike a target with a 26-foot margin of error, he said....