Iran's foreign minister headed to Russia on Sunday as peace efforts between Tehran and Washington hung in the balance, following a flurry of regional diplomacy and the collapse of planned talks in Pakistan.

Abbas Araghchi visited Oman between trips to Pakistani capital Islamabad and is expected to meet President Vladimir Putin on Monday, according to the Iranian ambassador.

On Saturday, US President Donald Trump scrapped a planned trip to Islamabad by his envoys Steve Witkoff and Jared Kushner.

In a sign that efforts were ongoing, the Fars news agency said Iran had sent "written messages" to the Americans via mediator Pakistan outlining red lines, including nuclear issues and the Strait of Hormuz.

Fars said the messages were not part of formal negotiations, however.

A ceasefire in the US-Israeli war with Iran has so far held, but its economic shockwaves continued to reverberate globally.

Iran has sealed off the strait, cutting flows of oil, gas and fertiliser and sending prices soaring, raising fears of food insecurity in developing countries.

Hopes for a second round of talks in Pakistan had centred on a planned visit by Witkoff and Kushner, but Trump cancelled the trip, dismissing it as "sitting around talking about nothing".

On Sunday, Trump told Fox News that if Iran wanted the talks, "they can come to us, or they can call us."

Trump faces domestic pressure as fuel prices rise following Iran''s closure of Hormuz, with midterm elections due in November. Polls show the war is unpopular among Americans.