An air strike killed 26 fighters of Iraqi paramilitary group Hashed al-Shaabi in eastern Syria after a deadly attack on US-led coalition troops in Iraq, a war monitor said Thursday.
Updating its toll for the Wednesday strike, the Britain-based Syrian Observatory for Human Rights said it was probably carried out by the coalition.
The coalition did not immediately provide comment.
Before the strike near the border town of Albu Kamal, rockets were fired at a military base north of Baghdad hosting coalition troops, killing two Americans and one Briton.
It was the deadliest such attack in years on an Iraqi military base hosting foreign troops.
There was no immediate claim of responsibility, but the United States has blamed Iran-backed factions from the Hashed al-Shaabi for similar violence in recent months.
Within hours, the air strikes were launched against Hashed forces just across the border in Syria.
Hardline Hashed factions have fought alongside Syrian government forces for several years and have been targeted by both coalition and Israeli air strikes.
The coalition has been carrying out air strikes in Syria since 2014, when IS overran a large swathe of the country and neighbouring Iraq.
Coalition-backed forces last year expelled the jihadists from their last outpost in eastern Syria, but the group retains sleeper cells on both sides of the border.