Efforts to resolve the conflict have hit an impasse, which the United States is trying to unlock with a naval blockade of Iran's oil exports. WASHINGTON/DUBAI, April 30 (Reuters) - Iran said on Thursday it would respond with “long and painful strikes” on U.S. positions if Washington renewed attacks and restated its claim to the Strait of Hormuz, complicating U.S. plans for a coalition to reopen the waterway. Two months into the U.S.-Israeli war with Iran, the vital sea channel remains closed,