WASHINGTON — The United States military struck targets in Iran on Tuesday, saying the attacks followed Iranian attempts to hit commercial ships and American forces in the Middle East, the Associated Press reported.

The strikes, and an earlier round on Sunday, ended a month without military action and raised the prospect of a full return to an intermittent war that has lasted more than six months. According to AP, the renewed fighting comes after President Donald Trump had appeared to shift towards pressing Iran through economic sanctions rather than force.

Writing on social media after US Central Command announced the latest strikes, Trump warned that "if the failed Nation of Iran retaliates for this very justified attack, they will be hit again at a much harder and higher level, but it will not be the biggest attack of them all, that is waiting in the wings."

Iran's Armed Forces General Staff and its joint military command said the country's armed forces would deliver what they described as "crushing and devastating blows" against the United States, AP reported.

Iranian state television said US forces had struck a fishmeal factory on Qeshm Island in the Strait of Hormuz, along with several civilian targets in Hormozgan province, including a fishing pier and a Ports and Maritime Organization tower in Sirik. Parrhesia News has not independently verified those claims, and the US military has not confirmed the specific sites.

The strait at the centre of the war

Both governments are contesting control of the Strait of Hormuz, the narrow waterway off Iran's coast through which about 20 per cent of the world's oil normally passes. Tehran effectively closed the strait after the war began.

The price of crude has risen more than 50 per cent this year, carrying fuel costs with it. AP reported that the average price of a gallon of regular petrol in the United States rose again overnight to $4.10, according to AAA, compared with $3.19 at the same point last year.

In Sunday's strikes, US Central Command said its forces had hit Iranian rocket launchers involved in placing sea mines in the strait. "U.S. forces took limited, precise action against IRGC minelaying forces posing an imminent threat in the Strait of Hormuz," the command said. "In essence, Iran created the threat and the U.S. military eliminated it to protect civilian mariners, commercial shipping, and the free flow of global commerce."

Iran responded to Sunday's attacks by launching missiles at US sites in Jordan, which were intercepted, while the United Arab Emirates said it had stopped an Iranian drone over its waters, according to AP.

A war with a domestic cost

Trump acknowledged on Monday that further strikes might be necessary. The renewed fighting is unfolding as US stockpiles of advanced interceptors have been drawn down and as the war has proved unpopular with many Americans, AP reported, with the conflict posing political difficulties for Republicans before November's midterm congressional elections.

A wider return to open conflict would carry significant risk for the region, where Iran has targeted US military bases and infrastructure in Gulf states since the war began.

Reporting attributed to the Associated Press. Casualty and damage claims from state media and combatant governments could not be independently verified.