Astana, Kazakhstan - The first day of Syria talks in Kazakhstan hit a snag as direct negotiations between rebels and the government looked unlikely, and as delegates sparred over details of a nationwide truce.

Representatives of the Syrian government and opposition on Monday traded barbs over interpretations of a ceasefire brokered by Russia and Turkey in late December, as their respective regional backers met behind closed doors to keep the meeting on track.

The meeting in Astana, organised by Russia and Turkey, is aimed at strengthening a nationwide ceasefire that has largely held despite pockets of violence across the country, and paving the way towards UN-led political negotiations in Geneva on February 8.

The talks mark the first time the Syrian opposition is represented solely by representatives of armed groups.

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Bashar al-Jaafari, head of the Syrian government delegation, accused the opposition of "misinterpreting" the tenets of the ceasefire, saying the "provocative tone and lack of seriousness in the opposition delegation chief's speech" had "irritated the attendees' diplomatic senses and experience".

Referring to the rebel delegation as "terrorists", Jaafari said opposition groups who signed the truce deal were "trying to undermine and sabotage the Astana meetings".

Opposition leader Yahya al-Aridi complained that the Syrian government had not demonstrated serious commitment to the ceasefire, which came into effect on December 30, arguing there should be "clarity" before direct negotiations.

"If there is seriousness in making these talks lead to something substantial, formality won't be that important," Aridi told Al Jazeera.

But as delegates exited closed-door talks to trade jabs via duelling press conferences, the crux of the meeting may have been happening elsewhere.

Noah Bonsey, a Syria analyst with the International Crisis Group, said any potential "impact" from the Astana talks is "more likely to come as a result of the trilateral talks between Iran, Turkey and Russia than it is from any direct exchanges between the Syrian delegations.

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"We're sitting on the sidelines of talks meant to be between the Syrian government and the opposition, but the main event is what is happening in the trilateral talks," he told Al Jazeera.

"Between Turkey, Russia and Iran you have tremendous leverage and military weight on the ground in Syria. If they make progress in adjusting the ceasefire that has already been agreed ... that could have major military ramifications."

Russia, whose 2015 military intervention was crucial in turning the tide in favour of the government, and Turkey, a prominent backer of the opposition, were key forces in establishing the ceasefire and bringing the opposing sides to Astana.

But diplomatic sources close to the opposition told Al Jazeera that the role of Iran, a key ally of the government in Damascus and backer of thousands of allied militia forces on the ground, has been problematic for the rebels within the talks.

The rebel delegation was reportedly hesitant to be seen sitting at the same table as the Iranian delegation and was angry that Iran could be named as the third guarantor - in addition to Russia and Turkey - in strengthening the ceasefire.

In separate press statements, officials from both sides made contrasting claims over whether Jabhat Fateh al-Sham, a group previously linked to al-Qaeda, is present in Wadi Barada.

The strategic area in rural Damascus is home to the capital's main water source. Recent violence there has threatened the fragile truce.

The ceasefire agreement stipulated that a truce would be implemented across all of Syria, excluding the parts of the country where Jabhat Fateh al-Sham and the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) are operating.

After the first round of talks on Monday, Jaafari said that the government's recent advances in Wadi Barada were aimed at driving out Jabhat Fateh al-Sham from the area, blaming the group for cutting water supplies to 5.5 million Syrians in Damascus since late December.

'Not present'

Rebel representatives in Astana refuted those claims, saying that government bombardment in the area was responsible for disrupting the water supply to the capital.

"Jabhat Fateh al-Sham are not present in Wadi Barada. We asked the Russians to go and see for themselves," Fares Bayoush, a Free Syrian Army commander, told a group of reporters.

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"We have evidence of the rockets which are still there ... These were Syrian rockets," he said.

But rebel leaders also said they "refused to look into the issue of Jabhat Fateh al-Sham until Syria had been emptied of all foreign fighters", referring to Iranian, Iraqi and Afghan groups fighting on behalf of the government - a demand not previously publicly mentioned as being within the provisions of the truce deal.