The Syrian Democratic Forces (SDF) said its commando academy at the al-Omar oil field in the eastern province of Deir al-Zour was hit in the early hours of Monday.

It accused Iran-backed militias of launching the drone from a nearby area controlled by Syrian government forces.

An Iran-backed militia umbrella group claimed it attacked the base on Sunday.

There was no comment or reports of casualties from the US military, which has about 800 troops in Syria to combat the Islamic State (IS) group.

It was the second incident since the US conducted strikes against Iran-backed groups in Iraq and Syria over the weekend in response to a deadly drone attack on a base in Jordan. The Pentagon confirmed to the BBC that there had been a rocket attack at its Mission Support Site Euphrates in Syria on Saturday, but there were no casualties or damages in the incident.

The SDF - which has controlled much of north-eastern Syria since defeating IS there in 2019, with the support of a US-led global coalition - said in a statement that six of its "commando fighters" were killed when a one-way attack drone targeted their training academy around midnight on Monday.

"Iranian-backed militias used the Syrian regime-controlled areas in Deir al-Zour as a staging ground for the terrorist attack," it alleged.

The SDF condemned the attack and asserted its "right to respond appropriately to the source".

The Syrian Observatory for Human Rights, a UK-based monitoring group, reported that seven SDF commandos were killed and 18 injured in what it said was the 108th militia attack on US bases in the country since mid-October.

The Islamic Resistance in Iraq (IRI) - an umbrella group of Iraqi militias believed to be armed, trained and funded by Iran - said it carried out a drone attack on Sunday "against the US occupation base in al-Omar oil field".

 The IRI has claimed many of the drone, rocket and missile attacks that have targeted US troops in Iraq, Syria and Jordan since the start of the war between Israel and Hamas in the Gaza Strip. It says that they are a demonstration of solidarity with the Palestinian people.

The attacks include the 28 January drone strike on the Tower 22 base near Jordan's border with Syria, which killed three US soldiers.

Iran denied any involvement in the attack, but the US believes it manufactured the drone and that co-ordination of the militias is overseen by its Islamic Revolution Guard Corps' (IRGC) Quds Force.

On Friday, the US struck more than 85 targets across seven facilities in Iraq and Syria used by the IRGC and affiliated militias, warning that it was just the "start" of its response to the Jordan attack.

The strikes in Syria killed 29 pro-Iran fighters, according to the Syrian Observatory for Human Rights. In Iraq, authorities said 16 people were killed.

Amid the heightened tensions in the region, US Secretary of State Antony Blinken is currently in Saudi Arabia as part of a Middle East tour, his fifth since the 7 October Hamas attacks on Israel.

Mr Blinken will visit Egypt, Qatar, Israel and the West Bank later this week, pushing officials to cut a new deal to free Israeli hostages and to help prevent an escalation of the conflict.

By David Gritten