US strikes in Syria aimed at Iran-backed forces: Biden

US President Joe Biden said Thursday that US air and artillery strikes that killed four militants in eastern Syria were ordered to protect US forces from attacks by Iran-backed militia.

"I directed the August 23 strikes in order to protect and defend the safety of our personnel . . . and to deter the Islamic Republic of Iran and Iran-backed militia groups from conducting or supporting further attacks on United States personnel and facilities," Biden said in a statement informing Congress of the action.

He said the US strikes, the heaviest action by American forces in the region in many months, responded to a series of rocket attacks on the facilities of US and partner troops in the area, including two on the al-Tanf Garrison and the Mission Support Site Green Village on August 15.

Biden said the retaliatory strikes, which involved Apache attack helicopters, AC-130 gunships and M777 artillery, targeted a facility used by the attackers for logistics and ammunition storage.

The first US strikes took place on Tuesday. But after the Iran-allied fighters launched a new barrage on US positions on Wednesday, a heftier force of American aircraft flew in to push back.

In total four militia fighters were killed and seven rocket launchers destroyed, the US Central Command, which oversees Middle East operations, said in a statement.

Three US service members incurred minor injuries in the shelling on Wednesday.

"We made a concerted decision … to provide a proportional response here from a deterrence standpoint," said Pentagon spokesman Brigadier General Patrick Ryder.

The strikes were over by early Thursday.

"We do not have anymore troops in contact. We believe this last round of escalation has terminated," a US official said on grounds of anonymity.

The fighting took place in Deir Ezzor, a strategic, oil-rich province bordering Iraq.

The area east of the Euphrates is dominated by the Kurdish-led Syrian Democratic Forces, allies of the United States and other coalition partners that are maintaining a mission against the remnants of the Islamic State jihadist group.

Tehran rejected US claims that it was behind the militia attacks on the American garrisons in Syria.

It says it only has Islamic Revolutionary Guard Corps positioned inside Syria as "military advisers" with pro-regime forces.

But Iraq's Kataeb Hezbollah, a pro-Iran group operating under the umbrella of the Hashed al-Shaabi network of militias, is involved inside Syria, as are the Iraqi Imam Ali Brigades and Sayyed al-Shuhada Brigades.

All three are close to the Revolutionary Guards.

The flare-up in attacks and counter-attacks came just as the United States and Iran near a possible deal to restore the 2015 nuclear deal, which could see the West ease sanctions on Tehran for it recommitting to strict limits on its nuclear program.

US officials say the fighting in Syria is not linked to the nuclear talks brokered by the European Union in Vienna.