Iran's top negotiator Mohammad Bagher Ghalibaf threatened a more forceful response to any further U.S. attacks after Tehran targeted American warships in their latest round of clashes.
The Iranian parliament speaker said that "the era of proportionate responses has come to an end".
"Any aggression against Iran's interests and security will receive a faster, more intense and more painful response," Ghalibaf said.
The exchanges of fire, which began with U.S. raids last week, come amid a deadlock in the six-month war between the two foes. Iran has maintained its stranglehold on the strategic Strait of Hormuz while Washington continues a counter-blockade of Iranian ports.
Washington is also seeking to choke Iran's economy, rolling out sanctions on entities with financial links to the Islamic republic in a bid to force it into submission.
