GENEVA (Reuters) - Syria’s chief negotiator at U.N. peace talks in Geneva on Friday delivered a 40 minute polemic attacking the political and armed opposition and their foreign backers, labeling them all “terrorists”.

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Fresh from a two-hour meeting with U.N. mediator Staffan de Mistura, which he said had focused primarily on combating terrorism, Bashar al-Ja’afari told reporters he would follow up on Saturday with another meeting, again all about terrorism.

De Mistura has said the agenda for the round of peace talks, expected to run until April 1, covers four topics: a new constitution, new elections, reformed governance, and counter-terrorism, included at Ja’afari’s request.

The first three topics are collectively supposed to ensure a political transition in Syria - anathema to Assad, who has ruled since the death of his father 17 years ago. Ja’afari said they would not be neglected, but terrorism needed to be the priority.

At the end of the last round of talks, his insistence on including terrorism appeared to be a potential mis-step, since the opposition had taken steps to distance itself from groups designated as “terrorists” by the United Nations, and now said they were fighting those groups.

At the same time U.N. investigators accused Syria’s government of committing atrocities by using chlorine gas and bombing schools, hospitals and the Damascus water supply.

But a new rebel offensive has been spearheaded by Tahrir al-Sham, an alliance of Islamist factions dominated by a group that was formerly al Qaeda’s official affiliate in the Syrian war.

The opposition has also previously blamed Syria’s government and its allies for breaking a ceasefire, which is supposed to be guaranteed by Assad’s allies Russia and Iran and by Turkey, which backs rebel groups in Syria.

Ja’afari said Turkish-backed rebel groups were now breaking the ceasefire, and coordinating with Tahrir al-Sham, proof they were supporting terrorism and showing why terrorism needed to top the agenda.

“Anyone who objects to such an approach would simply reveal their true face which is being a sponsor of terrorism,” he said.

He said the terrorist attacks had one goal, which was to undermine the peace talks.

Bashr al-Shami, the head of Tahrir al-Sham’s legislative council, appeared to confirm that his group wanted to derail the Geneva talks.

“To those who look for salvation for this oppressed people through conferences, the reality has proven that force can only be met with force ... and that these conferences are nothing but a mirage,” Shami said in a voice recording that Tahrir al-Sham circulated on social media.

Ja’afari, a veteran negotiator and Syria’s ambassador to the United Nations in New York, rattled off a list of “regimes” whom he deemed “sponsors of terrorism”: Turkey, Saudi Arabia, France, Britain, Qatar, Jordan and Israel.

He did not include the United States, which looks set to change its Syria policy under President Donald Trump to focus on defeating Islamic State and al Qaeda-linked groups rather than trying to unseat President Bashar al-Assad.