The global alliance - which usually strikes IS- for the first time hit regime-allied forces as they headed toward a remote coalition garrison near the southern border with Jordan, US officials said Thursday.
Syrian opposition delegation leader Nasr al-Hariri said it was not possible to reach a political solution or to fight terrorism as long as Iran and its militias remained in Syria, and reiterated the opposition's demand to remove President Bashar al-Assad.
The statement added that the US -led coalition forces will continue to defend themselves against Daesh or any other threat to the coalition or its allies in the area.
UN-mediated intra-Syrian talks are expected to end Friday merely three days after resuming on May 16, in line with what UN Syria envoy Staffan de Mistura said would be a short and business-like exercise.
United States officials said its military carried out the air strike on Thursday against militia supported by the Syrian government that posed a threat to American forces and US-backed Syrian fighters in the country's south.
In response to a question about the coincidence of the meeting with an American aggression and ISIL massacre against Syrians in addition to the ambition of achieving better results in this round, al-Jaafari said that the delegation discussed during today's session the US attack on one of the Syrian Arab Army's military points on al-Tanf road in the Syrian Badia, which took place Thursday evening.
Speaking to journalists shortly after the UN's announcement, Jaafari seemed to play down how much the expert meetings would push the constitutional process forward.
"The important thing is that our political ambition is higher because we want to focus on fighting terrorism represented by armed groups and the state and government terrorism happening against our country".
The reports gave different death tolls for the IS attack on the village of Aqarab al-Safiyeh in central Syria.
"It is utterly unacceptable and a violation of Syria's sovereignty", Russian news agencies quoted him as saying.
The Syrian Observatory for Human Rights, a monitoring group with activists on the ground, said the strike destroyed vehicles and killed eight militiamen.
In the first concrete results from talks this week on ending Syria's conflict, the United Nations said the warring sides had agreed to set up expert committees to discuss "constitutional issues".
Meanwhile, the Syrian opposition said in a statement it sought clarification on 13 points including the mandate of the body and its frame of reference. Hariri said the regime is not serious about discussing the political process of transition.
About US allegations about Sednaya prison, al-Jaafari said that this kind of allegation is not new and in every round of talks whether in Astana or in Geneva, and even before that, even in the Security Council, a massacre was carried out, adding that "only the nuclear weapon is left to hit us and they no longer have unsafe toys, but to use the nuclear and accuse us of using it".
The Syrian military official said on Friday that the area attacked was a military position along the Tanf highway in the desert. It said troops launched a counteroffensive under the cover of airstrikes.