Unleashed with joint US and Israeli air strikes on Iran almost two weeks ago, the war has so far killed about 2000 people and thrown global energy markets and transport into chaos.
The conflict has spread across the Middle East and prompted the International Energy Agency to plan a record release of strategic oil reserves to dampen one of the worst fuel shocks since the 1970s.
The United Nations Children's Fund (UNICEF) said more than 1100 children had been killed or injured.
At a campaign-style rally in Kentucky ahead of November midterm elections, Trump said the US had won the war but didn't want to have to go back every two years.
"We don't want to leave early do we?" he said on Wednesday. "We got to finish the job."
Oil prices, which shot up earlier in the week to nearly $US120 a barrel before settling back to around $US90, rose nearly five per cent on Wednesday and extended gains in Asian trade on Thursday amid renewed fears about supply disruption.
Iran has made clear it intends to impose a prolonged economic shock, with the spokesperson for Iran's military command saying in remarks directed at the US: "Get ready for oil to be $200 a barrel, because the oil price depends on regional security, which you have destabilised."
Iranian explosive-laden boats appear to have attacked two fuel tankers in Iraqi waters, setting them ablaze and killing one crew member after projectiles struck three merchant vessels in Gulf waters, port officials, maritime security and risk firms said on Thursday.
Iran also targeted fuel tanks at a facility in Bahrain's Muharraq, the interior ministry said.
Four people were wounded after two Iranian drones hit near Dubai International Airport in the United Arab Emirates, though flights continued, the Dubai Media Office said.
The International Energy Agency, made up of major oil-consuming nations, on Wednesday recommended releasing 400 million barrels from global strategic reserves to dampen one of the worst oil shocks since the 1970s, the biggest such intervention in history.
Trump said the IEA decision "will substantially reduce oil prices as we end this threat to America and the world".
US Energy Secretary Chris Wright said Trump had authorised the release of 172 million barrels from the US Strategic Petroleum Reserve from next week.
So far there has been no sign that ships can safely sail through the Strait of Hormuz, the now-blockaded channel along the Iranian coast that serves as a conduit for around a fifth of the world's oil.
On Wednesday, an Iranian military spokesperson said the Strait was "undoubtedly" under Iran's control and the G7 group of nations - the US, Canada, Japan, Italy, Britain, Germany and France - agreed to examine the option of providing escort for ships so they can navigate freely in the Gulf.
Trump said US forces had knocked out 58 Iranian naval ships and that Iran was "pretty much at the end of the line".
He said the US would now "look very strongly" at the Strait of Hormuz. "The straits are in great shape. We've knocked out all of their boats. They have some missiles, but not very many," he said.
US broadcaster ABC News said the Federal Bureau of Investigation had warned of Iranian drones potentially striking the US West Coast.
The US State Department also warned that Iran and aligned militias may be planning to target US-owned oil and energy infrastructure in Iraq and said militias had in the past targeted hotels frequented by Americans.
With AP
