Iran-backed Shiite militia leaders have vowed retaliation for the air strikes conducted by US against them along the Iraq-Syria border, which led to the death of four fighters.

Pentagon spokesman John Kirby said the US forces “conducted defensive precision air strikes against facilities used by Iran-backed militia groups in the Iraq-Syria border region”.

PMF groups have carried out several lethal attacks against US forces since the end of Iraq’s war with ISIS, in which they both played a key role.

Some PMF groups, including one targeted on Monday known as Kataib Hezbollah, have been in conflict with the US since around 2008, before the official formation of the PMF.

Mr Kirby said the strikes targeted two locations in Syria and one in Iraq that were “utilised by Iran-backed militias that are engaged in unmanned aerial vehicle [UAV] attacks against US personnel and facilities in Iraq”.

In addition to Kataib Hezbollah, another hardline pro-Tehran militia, Kataib Sayyid Al Shuhada, was among the “several Iran-backed militia groups” that had used the targeted facilities”, he said.

Syria’s state-run Sana news agency said a child was killed and at least three other people were wounded in the strikes.

Although the Iran-allied militias are officially part of the PMF, they implement Tehran’s foreign policy goal of ousting US troops from Iraq.

They increased their attacks on US assets in Iraq after the US drone strike on January 3 last year that killed Qassem Suleimani, the commander of Iran’s Islamic Revolutionary Guard Corps’ Quds Force.

Iraqi militia leader Abu Mahdi Al Muhandis and several aides were also killed in the attack outside Baghdad airport.

Since then, the militias have staged bomb, rocket and, more recently, drone attacks against military bases, logistics convoys and the US Embassy in Baghdad.

Two militia leaders, speaking on condition of anonymity, confirmed to The National that four Iraqi fighters were killed in the attacks that occurred at 2am.

“We are fully prepared and at the disposal of the General Command to retaliate,” said Ahmed Al Maksosi, the leader of the Kataib Sayyid Al Shuhada’s 14th Brigade.

PMF-linked lawmaker Ahmed Al Asadi, described the attack as “perfidious aggression” and said “the blood that was shed will turn into an Iraqi outrage against the aggressor”.