Syria's most important peace talks in 2 years have reached an 'impasse' - and they haven't even started yet

Syria's main opposition delegation, the Saudi-backed High Negotiating Council (HNC), has said it will not be attending peace talks over the country's future on Friday in Geneva, Reuters reported on Thursday.

The council will apparently continue to deliberate in the coming days and weeks over whether it will attend at all.

"UN says Syria talks will start as planned in Geneva tomorrow. The opposition team will not travel to Geneva tomorrow," Syria expert Charles Lister, a resident fellow at the Middle East Institute, said on Twitter.

That, he added, equals a major "impasse" before the talks have even begun.

The delegation's decision to skip the talks comes after its final calls for Syria's government to end its aerial bombardments on civilians and lift its sieges on rebel-held areas went unheeded by the UN's Syria envoy, Staffan de Mistura.

De Mistura had insisted at a press conference on Monday that "our line … is clear: no preconditions, at least to start the talks."

The HNC sent a letter to de Mistura and UN Secretary General Ban Ki-Moon reiterating its demands on Wednesday. It convened in Riyadh, Saudi Arabia, to await clarification from de Mistura over whether its preconditions would be met before Friday.

"There is a problem we would like to clarify with de Mistura," Riyadh Naasan Agha, a member of the HNC, told ABC. "Is the main aim of these negotiations for them to be held or to succeed?"

The UN, so far, has not reconsidered its position. And neither has the opposition.

"There must be a halt to the bombardment of civilians by Russian planes, and sieges of blockaded areas must be lifted" in order for conditions to be "appropriate" for meaningful negotiations, George Sabra, deputy head of the opposition delegation, told Reuters on Thursday.

The rebels claim that US Secretary of State John Kerry pressured them to attend the talks and threatened to cut off support to the rebels entirely if they did not show up in Geneva - a charge that Kerry has denied.

"The position of the United States is and hasn't changed. We are still supporting the opposition, politically, financially and militarily," he told reporters at a roundtable event Tuesday.

Jaysh al-Islam, one of the largest groups in the HNC, was quick to point out that the rebels have other sources of support besides the US.

"We do not forget that there are sisterly states that support us and help us overcome these pressures, particularly Saudi Arabia, Qatar, and Turkey," the group's spokesman, Islam Alloush, told Reuters in an email.

Indeed, opposition sources told the daily pan-Arab newspaper Al Hayat that the US had made "a scary retreat" in its position that the rebels would be unable to accept - namely, that Assad could run for reelection and there would be no set timetable for his departure.

That stands in contrast to the White House's previous position that while Assad does not have to go immediately, the timing of his departure should be addressed during negotiations.

Kerry apparently also signaled the Obama administration's endorsement of a four-point peace plan for Syria created by Iran, a staunch ally of Assad, and stipulated that the HNC has to include certain Moscow-friendly opposition leaders into its delegation. These included Kurdish PYD leader Saleh Muslim, former Syrian deputy Prime Minister Qadri Jamil, and Haitham Manna, exiled leader of the non-Islamist Syrian Democratic Council.

The Saudi-backed HNC refused to expand its delegation, insisting that it represents all legitimate opposition players. But a separate delegation made up of roughly 10 rebel leaders - including Kurdish representatives - proposed and endorsed by Moscow was invited to the talks anyway, in an "advisory" role.

The HNC's senior negotiator, Mohammad Alloush, initially promised a "strong reaction" to Kerry's demands, but did not immediately say whether the council would boycott the negotiations altogether.