Heraldo de Madrid - Rubio says expecting Iran response to US proposal on Friday

"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.

"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.

Following the start of the war with US-Israeli attacks on February 28, Iran largely closed the Strait of Hormuz and the US later imposed its own blockade of Iranian ports.

World markets had perked up and oil prices earlier this week amid hope that a Pakistani-mediated peace process would prolong a US-Iran ceasefire that began on April 8 and lead to a negotiated accord to end the conflict.

But stock markets sank again on Friday after an exchange of fire between Iranian and US forces in Hormuz, which fuelled fears renewed fighting could delay or derail the re-opening of the route.

Rubio said the US had been forced to respond to Iranian fire on its warships.

"We didn't fire, they fired on us," he said on Friday.

Iran's central military command has said that the clash had erupted when US vessels targeted an Iranian civilian tanker heading towards the Strait of Hormuz, and accused its foe of hitting civilian areas.

N.Carrasco--HdM