Pentagon said air strikes were carried out in retaliation for drone attack on US-led coalition base that killed a US contractor, injured another, and wounded five US soldiers.

The US attacks late on Thursday night were in retaliation for an attack against a US-led coalition base near Hassakeh in northeastern Syria at approximately 01:38pm (10:38 GMT) the same day, the Pentagon said in a statement.

US intelligence had assessed that the attacking drone was Iranian in origin. US Defence Secretary Lloyd Austin said the attacks targeted groups affiliated with Iran’s Islamic Revolutionary Guards Corps (IRGG) in eastern Syria.

“The airstrikes were conducted in response to today’s attack as well as a series of recent attacks against Coalition forces in Syria by groups affiliated with the IRGC,” Austin said in a statement.

Austin said he authorised the retaliatory strikes at the direction of US President Joe Biden.

“As President Biden has made clear, we will take all necessary measures to defend our people and will always respond at a time and place of our choosing,” Austin said.

“No group will strike our troops with impunity.”

US forces entered Syria in 2015, backing allied forces in their fight against the ISIL (ISIS) group.

The US maintains the base that was attacked near Hassakeh, while there are an estimated 900 US troops deployed in the country – and even more contractors – including in Syria’s north, south and east.

Overnight, videos on social media purported to show explosions in Syria’s Deir ez-Zor, a strategic province that borders Iraq and contains oil fields, the Associated Press reported.

Iran-backed militia groups and Syrian forces control the area, which has also seen suspected air attacks by Israel in recent months allegedly targeting Iranian supply routes.

Syria’s state-run SANA news agency did not immediately acknowledge any US strikes.

Syria’s mission to the United Nations did not immediately respond to a request for comment.

There was no immediate reaction from Iran over the strikes.

Two of the injured US troops were treated at the base in Syria while three other wounded US soldiers and the US contractor were evacuated to a coalition medical facility in Iraq, the US Defence Department said.

The number of casualties from Thursday’s drone attack – one killed and six injured – is highly unusual, even though attempted drone attacks against US forces in Syria are somewhat common.

General Erik Kurilla, who oversees US forces in the Middle East as the head of Central Command, said US troops have come under attack by Iranian-backed groups about 78 times since the beginning of 2021.

Kurilla, who testified to the US House of Representatives Armed Services Committee earlier on Thursday, cautioned about Iran’s fleet of drones.

“The Iranian regime now holds the largest and most capable unmanned aerial vehicle force in the region,” he said.

Three drones targeted a US base in January in Syria’s Al-Tanf region. The US military said two of the drones were shot down while the remaining drone hit the compound, injuring two members of the Syrian Free Army forces – part of the anti-ISIL coalition.

US officials believe drone and rocket attacks against its forces are being directed by Iran-backed militia in Syria.