UN mediator on Syria Staffan de Mistura attends a meeting with the Syrian opposition High Negotiations Committee (HNC) during Syria peace talks at the United Nations in Geneva, Switzerland, April 15, 2016.

The UN Special Envoy for Syria said on Thursday peace talks would continue next week, despite the main opposition’s decision to leave early, which he dismissed as “diplomatic posturing.”

Staffan de Mistura, in an interview with French-language Swiss television, said 400,000 people had been killed in the five-year-old war.

“We cannot let this drop,” he said. “We have to renew the ceasefire, we have to accelerate humanitarian aid and we are going to ask the countries which are the co-sponsors to meet.”

Previously, a source close to the High Negotiations Committee (HNC) said on Thursday that all members of the main Western-backed opposition will leave peace talks in Geneva by Friday.

“All members of the HNC will be leaving today and tomorrow,” the source told Reuters on Thursday, declining to be identified.

On Thursday, Syrian opposition negotiator Mohammad Alloush, representing Jaish al-Islam, a major rebel group, also said peace talks in Geneva could only resume if the government stopped massacres and released thousands of prisoners.

“We say to (government negotiator Bashar) Ja’afari if he wants a real national unity government, first he must release the 10,000 women in his prisons, and the tens of thousands more there,” Alloush said before leaving the Geneva talks.

“And (he must) stop the massacres he is committing everyday, so he can be a human with an ounce of nationalism. Then maybe the negotiations will resume,” he added.

The Syrian opposition started feeling uneasy about the peace talks when the fragile truce – currently taking place in Syria – started further crumbling.

On Tuesday, Syria’s main opposition chief lamented the fragile truce, calling for major powers to meet on the crisis, as his group left Geneva in protest against the escalating violence.

Head of the US and Saudi-backed opposition group, HNC, called on Tuesday for the UN Security Council to take firm actions against violators of the truce, which had been in place for about a month.

UN peace envoy Staffan de Mistura said Monday he had been informed by HNC that it would suspend its “formal participation” in the talks.

A Kremlin spokesman also said on Thursday President Vladimir Putin had held a domestic Security Council meeting at which he expressed concern over a “serious degrading of the situation” at Syrian peace talks in Geneva, TASS news agency reported.

Meanwhile, Syrian Prime Minister Wael al-Halaki said on Thursday that Damascus will hold a referendum on the constitution after the formation of a new government, Russian RIA news agency quoted him saying in an interview.

Syria accuses Europe, regional powers

In a defiant tone from Damascus after a halt to peace talks this week, Syria’s prime minister and foreign minister on Thursday accused European and regional powers of supporting terrorists and fueling fighting in the country.

Halaki said Saudi Arabia, Qatar, Turkey, Britain and France did not want a political solution to the conflict.

“These regimes are working to escalate terrorist actions, support terrorists and destroy the cessation of hostilities agreement agreed by Russia and the United States,” state news agency SANA quoted him as saying.

Foreign Minister Walid al-Moualem said earlier that states including Turkey continued to supply rebels in Syria with advanced weapons, and that the Syrian government would press on with its fight against terrorists.

The partial truce, brokered by Washington and Moscow in February, initially reduced violence in the west, but fighting has picked up again in recent weeks, leaving the ceasefire in tatters.

The statements from Damascus suggested it still felt it was in a position of strength, bolstered by a six-month-old Russian military intervention on President Bashar al-Assad’s side.

A top adviser to Assad said that “dialogue, local agreements and destroying terrorism” were the way to ensure a political solution to the conflict.

“We are trying to exploit every possible opportunity for the success of the political solution to the Syrian crisis,” Bouthaina Shaaban said.

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