The strikes - which took place at roughly 1.30am GMT - come as a response to a number of drone and missile attacks against US bases and personnel in Iraq and Syria since 17 October.

They were carried out using two F-16 fighter jets using precision munitions, and targeted weapons and munition storage facilities near Abu Kamal, a Syrian town on the border with Iraq, a US official said.

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The strikes reflect the determination of the US government to maintain a balance and deter any further aggression, possibly fuelled by Israel's war against Hamas.

The US has 900 troops in Syria and 2,500 in Iraq, but there is growing concern they could become targets if the conflict spreads throughout the Middle East.

According to the Pentagon, there have been at least 19 attacks on US bases and personnel in Iraq and four in Syria since last week.

Air Force Brigadier General Pat Ryder said 21 US personnel were injured in two of those assaults that used drones to target al Asad Airbase in Iraq and al Tanf Garrison in Syria.

In a statement, Defence Secretary Lloyd Austin said the strikes are a "response to a series of ongoing and mostly unsuccessful attacks" by Iranian-backed militia groups.

"If attacks by Iran's proxies against US forces continue, we will not hesitate to take further necessary measures to protect our people."

He said the US holds the capital Tehran responsible for funding, arming, equipping and directing the proxies.

Mr Austin said President Joe Biden directed the narrowly tailored strikes "to make clear that the United States will not tolerate such attacks and will defend itself, its personnel, and its interests".

He added that the operation was separate and distinct from Israel's war against Hamas.

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Although the US has not accused Iran of having a direct role in the 7 October attack on Israel by Hamas militants, it has noted that Iran has long supported the militant group.

Likewise, Iranian officials have openly criticised the US for providing Israel with weapons that have been used to strike Gaza.

It is not the first time the US has carried out retaliatory strikes against Iranian-backed forces.

Back in March, the US struck sites in Syria used by groups linked to Iran's Revolutionary Guard, after a US contractor was killed and seven injured after an Iranian-linked attack in northeast Syria.

US officials have routinely stressed that the American response is designed to be proportional, and is aimed at deterring strikes against US personnel who are focused on the fight against the Islamic State group.