With a US deadline approaching, the United States and Iran have received the framework of a plan to end their five-week-old conflict, though Tehran rejected any immediate move to reopen the Strait of Hormuz.
President Donald Trump has threatened to rain "hell" on Tehran if it did not make a deal by the end of Tuesday that would allow traffic to start moving again through the vital route for global energy supplies.
The Pakistani-brokered plan emerged from intense overnight contacts and proposes an immediate ceasefire, followed by negotiations on a broader settlement to be concluded within 15 to 20 days, a source aware of the proposals said on Monday.
Pakistan's army chief, Field Marshal Asim Munir, was in contact "all night long" with US Vice-President JD Vance, special envoy Steve Witkoff and Iranian Foreign Minister Abbas Araqchi, the source said.
Iran's foreign ministry said on Monday that Tehran had formulated positions and demands based on its interests and communicated them through intermediaries, in response to ceasefire proposals.
Ministry spokesman Esmaeil Baghaei said details of the response would be announced in due time, but added negotiations were "incompatible with ultimatums and threats to commit war crimes".
Earlier on Monday, a senior Iranian official told Reuters that Iran would not reopen the strait as part of a temporary ceasefire, nor would it accept deadlines or pressure to reach a deal.
Washington was not ready for a permanent ceasefire, the official said.
Axios first reported on Sunday that the US, Iran and regional mediators were discussing a potential 45-day ceasefire as part of a two-phase deal that could lead to a permanent end to the war.
Later on Sunday, the president in a follow-up post gave a more precise deadline: "Tuesday, 8:00 P.M. Eastern Time! (10am AEST on Wednesday)"
Fresh aerial strikes were reported across the region on Monday, more than five weeks since the US and Israel began pounding Iran in a war that has killed thousands and damaged economies by boosting oil prices.
Iranian state media said the head of the Revolutionary Guards' intelligence organisation, Majid Khademi, had died.
Israel on Monday claimed responsibility for his death.
Israel and the US have carried out assassinations of Iran's leaders since the start of the war on February 28, killing several high-ranking members of the Iranian ruling system, including supreme leader Ayatollah Ali Khamenei, who was replaced by his son, Mojtaba.
A US-Israeli attack hit the data centre at Sharif University of Technology in Tehran, damaging infrastructure underpinning the country's national artificial intelligence platform and thousands of other services, Fars News Agency said on Sunday.
Israeli Defence Minister Israel Katz in a statement threatened to destroy Iran's infrastructure and hunt down its leaders "one by one".
Trump has repeatedly warned Iran he could expand US strikes to include civilian infrastructure, such as power plants and bridges.
Experts say such attacks could constitute war crimes but the International Criminal Court lacks jurisdiction because the countries involved are not members of the court.
Iranian weekend strikes on petrochemical facilities and an Israeli-linked vessel in Kuwait, Bahrain and the UAE underscored the country's ability to fight back despite Trump's repeated claims to have knocked out its missile and drone capabilities.
Iran responded to the attacks launched by the US and Israel in February by effectively closing the Hormuz waterway, a conduit for about a fifth of the world's oil and natural gas supply, and attacking Israel, US military bases and energy infrastructure around the Gulf.
At least four Israelis were killed in a missile attack on a residential building in Haifa in northern Israel overnight, Israeli emergency service MDA said on Monday.
Israel has also invaded southern Lebanon and struck Beirut in a fight against Iran-backed Hezbollah militants that has become the most violent spillover of the US-Israeli war on Iran.