The US says it has hit "dozens" of Iranian military targets in overnight attacks, in response to Iran hitting commercial ships in the Strait of Hormuz.
No commercial vessels have crossed the vital waterway since yesterday evening, according to ship-tracking data - eight crossed on Sunday, down from 21 on Saturday.
The US military says it struck "air-defense systems, coastal radar sites, missile and drone capabilities, and small boats", using aircraft, ships, and drones - including "one-way attack sea drones for the first time".
In response, Iran says it targeted US bases in Jordan, Bahrain, and Kuwait, and also radar systems in Oman.
Last week, Donald Trump said the US-Iran ceasefire was "over" - adding that Iran's leadership were "scum".
On Sunday, President Donald Trump told NBC Iran had agreed to a deal with the US during talks over the weekend.
He said: "They agreed to a deal yesterday, a perfect deal for us. No nuclear, no this, no that, no nothing. They gave up everything."
On Monday, Iran's foreign ministry spokesman called Trump's comments "absolutely untrue".
Esmail Baghaei says no topic other than the Strait of Hormuz was discussed during a meeting between the two countries in Oman on Saturday.
Mediators are continuing their efforts in negotiations between the US and Iran, he adds.
Iran's foreign ministry spokesman says the US-Iran deal has "entered a crisis".
Iranian state media quotes Esmail Baghaei as saying Iran's "defensive strikes" are solely against bases and facilities used by the US to attack the country.
"We will not hesitate in our self-defence," he adds, saying Iran cannot allow the US to use transit in the Strait of Hormuz to harm the country's sovereignty and security.
Baghaei says negotiations on Saturday were solely focused on the vital waterway, adding that Iran's goal was to ensure the safe passage of ships. But, he says, US pressure on Oman has hindered efforts.
As a reminder, ship-tracking data shows no vessels have transited the strait since yesterday evening.
On the memorandum of understanding - a 14-point deal signed on 17 June - Baghaei says Iran will not execute its commitments if the US fails to honour the agreement.
