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 tackle more complex issues including Iran's nuclear program.
Iranian media reported that the country's negotiators had been pushing for the memorandum to include the release of billions of dollars of frozen assets at talks in Qatar.
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, fertiliser 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 futures rose by about 3.5 per cent on Tuesday to around $US100 ($A140) a barrel.
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 defence 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 Ayatollah 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 Islamic 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.
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, returned to Iran from Qatar after talks seeking agreement on the release of around $US24 billion ($A33 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 finalised.
As part of any initial deal, Iran also wants a stop to the conflict in Lebanon, where a mid-April ceasefire has failed to halt fighting between Israel and Iran-backed militant group Hezbollah.
Israeli Prime Minister Benjamin Netanyahu said in a statement on Tuesday that Israel was "deepening its operations in Lebanon", saying the military "is operating with large forces in the field".
