Iran said the United States had violated a ceasefire after the US conducted what it called defensive strikes in southern Iran, while US Secretary of State Marco Rubio said negotiating a deal to halt the conflict could "take a few days".
Iran's foreign ministry said US strikes in Iran's southern Hormozgan province, where Iranian media reported sounds of explosions early on Tuesday, represented a "gross violation" of a tenuous ceasefire in place for nearly seven weeks.
Both sides had previously indicated progress on a memorandum of understanding that could halt the war and restart shipping through the blockaded Strait of Hormuz, while giving negotiators 60 days to negotiate more complex issues including Iran's nuclear program.
Iranian media reported that Iran's negotiators had been pushing for the memorandum to include the release of billions of frozen assets at talks in Qatar.
OIL RISES AGAIN
Following strikes against targets that the US said included boats attempting to lay mines and missile launch sites, Rubio told reporters on his plane in India's Jaipur that the Strait of Hormuz had to be open "one way or the other".
The war, which began with US and Israeli strikes on Iran on February 28, has caused an unprecedented oil supply shock, pushing up the costs of fuel, fertilizer and food. Iran responded to the strikes by launching drones and missiles at Gulf states that host US bases.
Traffic through the Strait of Hormuz, which normally carries about a fifth of global trade in oil and liquefied natural gas, has been a fraction of its usual level since the war began.
Global benchmark Brent crude oil rose about 3.5% on Tuesday to more than $99 a barrel following news of the US strikes.
'CLOCK CANNOT BE TURNED BACK'
US Central Command said late on Monday it had carried out the fresh strikes designed "to protect our troops from threats posed by Iranian forces."
Iran's Revolutionary Guards said on Tuesday they reserved the right to retaliate. They said air defense units had downed a US drone and fired at another drone and a fighter jet which they said had entered Iranian airspace over the Gulf region.
In comments posted on his Telegram channel on the occasion of the annual hajj pilgrimage, Iran's Supreme Leader Mojtaba Khamenei said: "The clock cannot be turned back, and the nations and lands of the region will no longer be a shield for American bases."
"From now on, the slogans 'Death to America' and 'Death to Israel' will be the slogans of the nation and the oppressed people of the world, especially the youth," he added.
US President Donald Trump has previously cited the slogans while justifying military action against Iran.
Trump had said talks with Iran were going "nicely" in a lengthy post on Truth Social on Monday, but warned of attacks if they failed. It "will only be a Great Deal for all, or no Deal at all," he wrote.
DOHA TALKS
Iranian and US officials have indicated that recent indirect talks made progress on a memorandum of understanding, or initial deal, that would lead to further negotiations over a final agreement.
Iran's top negotiator, Mohammad Baqer Qalibaf, its foreign minister and its central bank governor were in Doha on Monday for talks with Qatar's prime minister on a potential deal, an official briefed on the visit said.
Qalibaf returned to Iran after seeking agreement on the release of around $24 billion of frozen Iranian funds as part of the memorandum of understanding, Iranian media reported.
Iran's Fars news agency cited a source saying that the unfreezing of the funds was the last serious sticking point for the memorandum of understanding to be finalized.
According to Iranian sources, an initial deal would cover ending the war on all fronts, establishing a 30-day framework for restarting movement through the Strait of Hormuz, and possibly providing some financial relief - with more complex issues such as Iran's nuclear program to be negotiated in a second phase.
Iran has been letting some ships through the strait, giving preference to vessels linked to countries with which it has alliances or close ties, and striking government-to-government agreements, Reuters has reported.
Trump has said his key aim in the war is to prevent Iran from developing a nuclear weapon with its highly enriched uranium. Tehran denies any such plans.
After a warning of escalated strikes, Israeli forces had expanded their operations in southern Lebanon, Israeli media reported on Tuesday.
Thousands have been killed in the wider conflict, mostly in Lebanon and Iran. Inside Iran, internet monitoring group Netblocks reported a partial restoration of connectivity after a near 90-day blackout.
