US Secretary of State Marco Rubio said Washington was expecting a response from Iran on Friday to US proposals for a deal to end the conflict.
"We're expecting a response from them today at some point... I hope it's a serious offer, I really do," Rubio told reporters during a visit to Rome.
"The hope is it's something that can put us into a serious process of negotiation," he said.
He also slammed as "unacceptable" efforts by Iran to control the Strait of Hormuz, following a report that Tehran has created an authority to approve transit through the vital waterway.