"The paper that has been presented is put aside for now", Naser al-Hariri, chief negotiator of the Turkish and Saudi-backed High Negotiations Council (HNC) told reporters Thursday, making reference to the UN's proposed plans to write a new Syrian constitution.
A USA airstrike struck pro-Syrian government forces that the coalition said posed a threat to American troops and allied rebels operating near the border with Jordan on Thursday, the first such close confrontation between US forces and fighters backing President Bashar Assad.
Officials said the strike near Tanf hit a tank and a bulldozer and forces there, but it was not clear if they were Syrian army troops or other pro-government allies.
Tuesday's start of talks in Geneva were overshadowed by US accusations that the government in Damascus carried out mass killings at a prison near the Syrian capital and then burned the victims' bodies in a crematorium.
The "defensive" strike was also an apparent signal to Assad to keep his forces out of a zone where USA -backed rebels are fighting the Islamic State group.
"Sultan Murat, Faylak ash-Sham, Jaysh as-Thawra, Jaysh Yarmouk, Harakat Tahrir Watan and Coalition of south forces, Ahrar ash-Sham and Shamiyya Front have chose to freeze participation in the negotiations delegation starting from today, " the paper dated of May 18 reads.
The officials weren't authorized to speak publicly on the matter and demanded anonymity. The U.S.is backing Syrian Kurdish forces who are also fighting IS to the country's east.
United Nations envoy says discussions begin on constitutional process amid efforts to end Syria's civil war.
He added that the constitution was "the exclusive right of the Syrian people, and we do not accept any foreign interference in it".
Meslet, who spoke at a demonstration outside of the U.N. Geneva compound led by female relatives of prisoners held in Syria, said the proposal involved "the constitutional frame" for an eventual transition period in Syria.
The Islamic State group has launched an offensive against government forces in central Syria near the highway that links the capital Damascus to the northern city of Aleppo.
State TV said two people were wounded in IS shelling on the nearby town of Salamiyeh.