US President Donald Trump vowed to hit back hard at Iran after it attacked US bases in Jordan on Wednesday, as the Middle East war reignited and once again drew in the Islamic republic's proxies.

The warning came after a lull in the fighting -- that had spurred hopes of a return to negotiations -- appeared to end, sending oil prices jumping five percent over fears of disruptions to global supplies.

On Wednesday, Saudi Arabia and the United States announced strikes on militant bases in Iraq, while US ally Israel accused Iran-backed Hezbollah of a truce violation.

For two days, the world's biggest oil exporter Saudi Arabia has reported drone attacks targeting crude facilities that it blamed on Iraqi armed groups allied with Tehran.

Iran meanwhile launched missiles at US ally Jordan, with state media later reporting an American attack near the Islamic republic's border with Iraq.

"We'll be hitting them hard. They're going to get a beating," Fox News's correspondent quoted Trump as saying, adding that the US president swore for emphasis: "We are going to beat the 'effing s' out of them."

'War by other means'

Saudi security analyst and researcher Hesham Alghannam told AFP: "Tehran is now using its proxy network to sustain leverage while the diplomatic track absorbs international attention. 

Iran's state television, meanwhile, reported a US strike in the Piranshahr border area, after the Fars news agency quoted an official in West Azerbaijan province as saying a missile hit an uninhabited area, leaving no casualties. 

Earlier, Jordan's army said it had intercepted five Iranian missiles, with Iran's Revolutionary Guards saying they had targeted US bases there.

"As long as the threats against the Islamic Republic of Iran continue... the resistance will continue," they added.

On another front, US ally Israel accused Hezbollah of firing a drone overnight at an Israeli vehicle inside Lebanon, in what the military called "a blatant violation of the ceasefire".

Israel fought alongside the US in the first weeks of war against Iran, while battling Hezbollah in Lebanon, but it has yet to join the latest round of strikes against the Islamic republic.

'Dangerous'

In Iraq, a joint US-Saudi air operation followed attacks by what Riyadh called "terrorist militias loyal to Iran" on its oil facilities. 

The US military said logistics and weapons sites belonging to an Iran-aligned group were targeted in the strikes.

According to Iraq's Hashed al-Shaabi alliance, the attacks killed at least 20 of its members across seven provinces, including Baghdad.

It denounced a "dangerous escalation" against an "official security institution".

Two Hashed officials said five Iranian advisors were among those killed, and AFP correspondents saw coffins draped with Iranian flags. 

The Hashed al-Shaabi alliance, also known as the Popular Mobilisation Forces, was created in 2014 to fight jihadists before it was formally integrated into the armed forces. 

It includes brigades belonging to Iran-backed groups reputed for acting unilaterally.

Iraq denounced the US-Saudi strikes and said it rejects "all acts of aggression, regardless of the party responsible or the justifications presented".

The Ministerial Council for National Security said it would "confront any violation of Iraq's sovereignty, and prevent any source from using Iraqi territory to threaten neighbouring states".

According to Fox News, however, Trump said the strikes were "coordinated with the Iraqi government".

The strikes follow growing US pressure on Iraq to disarm pro-Iran groups. Earlier this month, Prime Minister Ali al-Zaidi visited both the US and Iran.

Red Sea

The US had said the days-long cessation in fighting was aimed at kickstarting a new round of negotiations, including over the Strait of Hormuz, which Iran has blockaded throughout much of the war.

The Revolutionary Guards said they had attacked and stopped three tankers in the strait, insisting Iran has "full control" of the waterway, which was open and free to transit before the war.

Tehran has insisted it will retain control of the crucial conduit for energy shipments, and has also announced plans to collect fees for passage, which Washington opposes.

The US also announced new sanctions targeting entities linked to Iran's Guards that it accused of extorting ships transiting the strait.

The Hormuz closure has lent greater significance to the Red Sea, the only other maritime route for oil shipments from Saudi Arabia.