President Donald Trump said on Tuesday the war would be over "very quickly" while Vice President JD Vance talked up progress in talks with Tehran about an agreement to end hostilities.
"We're in a pretty good spot here," Vance told a White House press briefing.
Trump made his comments a day after saying he had paused a planned resumption of hostilities following a new proposal by Tehran to end the conflict.
"I was an hour away from making the decision to go today," Trump told reporters at the White House.
Iran's leaders are begging for a deal, he said, adding that a new US attack would happen in coming days if no agreement was reached.
The United States has been struggling to end the war it began with Israel nearly three months ago.
Trump has repeatedly said during the conflict that a deal with Tehran was close, and similarly threatened heavy strikes on Iran if it did not reach an accord.
The US president is under intense political pressure at home to reach an accord that would reopen the Strait of Hormuz - a key route for global supplies of oil and other commodities.
Gasoline prices remain high and Trump's approval rating has plummeted with congressional elections looming in November.
The conflict has caused the worst-ever disruption to global energy supplies, blocking hundreds of tankers from leaving the Gulf while damaging energy and shipping facilities across the region.
Two Chinese ships, among a handful of supertankers carrying Iraqi crude, exiting the Gulf this month, passed through the narrow strait carrying around four million barrels of crude, according to data from LSEG and Kpler.
Oil prices eased on the positive signals from the White House and in the Gulf, with Brent crude falling to as low as $US110.16 ($A155.22) a barrel, before regaining much of its losses.
"Investors are keen to gauge whether Washington and Tehran can actually find common ground and reach a peace agreement, with the US stance shifting daily," said Toshitaka Tazawa, an analyst at Fujitomi Securities.
Speaking to reporters at a White House briefing, Vance acknowledged difficulties in negotiating with a fractured Iranian leadership.
"It's not sometimes totally clear what the negotiating position of the team is," he said, so the US is trying to make its own red lines clear.
One objective of Trump's policy is to prevent a nuclear arms race from spreading in the region, he said.
Ebrahim Azizi, head of the Iranian parliament's national security committee, said on X that Trump's pausing of an attack was due to the realisation that any move against Iran would mean "facing a decisive military response".
Iranian state media said Tehran's latest peace proposal involves ending hostilities on all fronts including Lebanon, the exit of US forces from areas close to Iran, and reparations for destruction caused by the US-Israeli attacks.
Tehran also sought the lifting of sanctions, release of frozen funds and an end to the US marine blockade, according to Deputy Foreign Minister Kazem Gharibabadi as cited by IRNA news agency.
The terms as described in the Iranian reports appeared little changed from Iran's previous offer, which Trump rejected last week as "garbage".
