A strike on Thursday by an alleged drone (drone) Iranian-made missile killed an American contractor and wounded six other Americans in northeastern Syria and the American forces retaliated with air strikes at locations in Syria used by groups linked to Iran’s Revolutionary Guards, the Pentagon said. Activists said the US bombing killed at least four people.

While not the first time the US and Iran have traded blows in Syria, the attack and the US response threaten to derail recent efforts to de-escalate tensions in the wider Middle East, which rival powers have taken steps towards recession in recent days after years of turmoil.

US Defense Secretary Lloyd Austin said the US intelligence community had determined the drone was of Iranian origin, but offered no other direct evidence for that claim. The drone struck a coalition base in the northeastern Syrian city of Hasakah. The injured include five American servicemen and one American contractor.

Austin said the strikes were in response to the drone strike “as well as a series of recent attacks against coalition forces in Syria” by groups linked to the Revolutionary Guard.

Iran relies on a network of proxy powers through the Middle East to counter the US and Israel, its arch-nemesis. The US has had forces in northeastern Syria since 2015, when it was deployed as part of the fight against Islamic State, and maintains about 900 troops there, working with Kurdish-led forces that control about a third of Syria.