Halting violence and terrorism in Syria was among the terms of the never-implemented "Geneva I" declaration made by an international conference here in 2012, and which forms the basis for the current talks.
The Syrian regime is spotlighting hardline Islamists groups among the rebels and therefore slapping the "terrorist" label on the broader opposition. Government negotiators repeatedly have insisted that the subject of terrorism must be foregrounded at the talks.
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As meetings got under way in Switzerland last week, Syrian officials brandished what they said was a list of rebel terrorist acts and lambasted countries such as the Arab monarchies and Turkey which are top backers of the opposition.
"We have to combat more than 83 countries that are interfering daily in the internal affairs of the Syrian Arab Republic, sending arms, sending weapons, sending terrorists and sending all that is destroying Syria," Deputy Foreign Minister Faisal Muqdad said in Geneva earlier this week.
Among the groups in the regime's spotlight is the al-Qaeda-linked Islamic State of Iraq and the Levant (ISIL).
The mainstream rebels of the Free Syrian Army underline that they themselves are fighting the jihadists, while the Turkish army said yesterday it had destroyed an ISIL convoy after coming under fire near the Syrian border.
The opposition meanwhile had "prepared a massive file on the regime's terrorism with irrefutable evidence and documents," a source in its delegation told AFP.
It pointed to the use of chemical weapons and explosive-packed "barrel bombs".
It also demanded that the talks address the role of Lebanese militia Hezbollah -- backed by key Assad ally Iran -- classed as a terrorist group by Western nations.
In addition, it said Syrian pro-regime militias must be held to account.
Speaking yesterday, opposition spokeswoman Rafif Jouejati had told AFP that the regime's talk of terrorism was part of its "diversionary tactics".
"Of course everybody's concerned about terror. We know that the Free Syrian Army has declared war on al-Qaeda and ISIL," she said.
"We have rather compelling evidence of collusion between the Assad regime and ISIL and al-Qaeda operatives. We know that the Assad regime released al-Qaeda operatives and unleashed them on our people," she added.