US Secretary of State Marco Rubio has 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 on Friday 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.
"Iran now claims that they own, that they have a right to control, an international waterway... That's an unacceptable thing that they're trying to normalise," Rubio told reporters during a visit to Rome.
No decisions yet on withdrawing from NATO
Rubio also said that President Donald Trump has yet to decide how to respond to some allies denying the US military the use of their bases in its war on Iran.
Rubio was asked about that threat and the possibility of the US withdrawing from the NATO military alliance.
"If one of the main reasons why the US is in NATO is the ability to have forces deployed in Europe that we could project to other contingencies, and now that's no longer the case, at least when it comes to some NATO members, that's a problem, and it has to be examined," he told reporters.
He added that "ultimately that's a decision for the president to make", adding: "He hasn't made those decisions yet."
He said the announcement to withdraw 5,000 troops from Germany was "already pre-programmed" and signalled a return to 2022 levels.
"We have global obligations all over the world. We have troop deployments all over the world. And those are constantly shifting and changing," he added.
"That's a decision the president has to make, especially within the context of recent developments by some countries within NATO and the stance they've taken towards the United States.”
Allies’ denial of using military bases
Trump has threatened to pull US troops from Italy and Spain due to their opposition to the Iran war, with Madrid notably refusing to allow the use of its bases.
Italy also recently refused authorisation for some US aircraft headed to the Middle East on a combat mission to land at its Sigonella base, a defence ministry source and Italian media said on Tuesday.
Under the terms of agreements with the United States, some Italian bases can be used by US military aircraft, but only for logistical purposes.
Trump has threatened to slash US troop numbers in Germany and other European allies during both his White House terms, saying he wants Europe to take on greater responsibility for its defence rather than depending on Washington.
He now appears determined to punish allies who have failed to back the US in the Middle East war or contribute to a peacekeeping force in the crucial Strait of Hormuz waterway, which Tehran's forces have effectively closed.
