The war, which began on February 28 with a wave of US-Israeli strikes on Iran, was paused by the April truce, but efforts to hammer out a permanent end to the fighting have stalled, and sporadic exchanges of fire have put the ceasefire under repeated strain.

In their second straight day of tit-for-tat attacks, Washington hit surveillance, communications and air defence facilities, US Central Command (CENTCOM) said, while Iran's Revolutionary Guards announced a "punitive operation" targeting a US base in Jordan and Gulf states reported incoming fire.

Mediators Pakistan and Qatar suggested backchannel efforts to negotiate an end to the war were ongoing in spite of the flare-up, though Islamabad cautioned it was "hard to be an optimist" in light of the latest escalation.

The strikes took place while a Qatari delegation was in Tehran, with a diplomatic source saying the discussions were "conducted in coordination with the United States".

US President Donald Trump, who has repeatedly maintained negotiations with Tehran were close to a deal, said on Wednesday that Iran keeps "playing us for suckers" and will now "have to pay the price".

Hours after, CENTCOM said US forces began strikes early Thursday on Iran in response to its "unwarranted and continued aggression", later adding it had completed its attacks.

Iranian media reported explosions across the south, with at least three people wounded in Tehran province.

Jordan said it had shot down 20 Iranian missiles, while Kuwait's military said its air defences had engaged "hostile aerial targets".

Bahrain, which hosts a US naval base, said an 11-year-old girl suffered minor injuries and homes and cars were damaged by "sinful Iranian aggression".

- 'Negotiate with bombs' -

The renewed hostilities came as Pentagon chief Pete Hegseth said that if Trump required it, "we'll negotiate with bombs".

Iran's foreign ministry said on Thursday that "the illegal and criminal attacks perpetrated by the United States in recent hours not only constitute a flagrant violation... but also render the ceasefire practically meaningless".

Mediators, however, were keeping up diplomatic efforts, with a team of Qatari negotiators departing Tehran following talks "that lasted into the early hours of this morning", the diplomat said.

A foreign ministry spokesman for fellow mediator Pakistan, which hosted an initial round of talks between the warring parties, said it had not "lost hope" in a negotiated resolution.

Still, said Tahir Andrabi, "It is hard to be an optimist in the new exchange of hostilities."

Saudi Arabia, which also came under Iranian attack during the war, called on Thursday for more talks under Pakistani and Qatari mediation.

China, the biggest buyer of Iranian oil, likewise called for more negotiations on Thursday, with a foreign ministry spokesperson urging the warring parties "to immediately cease military operations... respond to the mediation efforts of relevant countries, and achieve a comprehensive and lasting ceasefire".

- Hormuz threatened -

Iran has renewed its warnings over the Strait of Hormuz, a vital waterway for oil and gas transport which it has essentially closed.

"Are you making the sacred Strait of Hormuz unsafe?! We will make the region hell for you," Majid Mousavi, the head of the Iranian Guards' aerospace force, said in a social media post.

On Wednesday, three Indian sailors on a commercial vessel were killed when the United States attacked the ship off the coast of Oman, New Delhi's shipping minister said Thursday.

India's foreign ministry summoned a top US diplomat in New Delhi after the attack on the MT Settebello to lodge "a strong protest".

The Iranian navy said it had also hit two ships trying to sail through the strait, state television IRIB and the Mehr agency reported.

Another Iranian news agency, Tasnim, quoted the country's military operational command as saying the crucial waterway was "completely closed" and that "any vessel traffic" there would be targeted.

But CENTCOM denied that, saying "commercial ships are continuing to transit in and out of the Strait of Hormuz tonight".

- 'Bomb the S out of them' -

Earlier, American broadcaster Fox News reported that Trump said Iranian leaders had called him directly in the White House Situation Room as the US bombs began falling.

Iran's Guards quickly denied Tehran had done so, the IRNA news agency said.

Fox reporter Trey Yingst, who spoke to Trump, quoted the president as saying that if Iran did not accept US terms for ending the war, "We'll bomb the S out of them tomorrow night".

"We were really close to a deal, but they keep tapping us along," Trump told reporters Wednesday morning.

Hegseth suggested the strikes could extend into a third night, saying they would be "strong" and "clear".

burs-smw/dcp