BEIRUT/GENEVA: The UN special envoy for Syria has vowed to take fragile peace talks into next week despite a walkout by the main armed opposition, a breakdown in a truce and signs that both sides are gearing up to escalate the five-year-old civil war.

Staffan de Mistura, who dismissed the opposition’s departure as “diplomatic posturing,” expected the delegation to return to the negotiating table. The opposition declared a “pause” this week because of a surge in fighting and too little movement from the government side on freeing detainees or allowing in aid.

Asked whether talks would carry on, de Mistura said on Thursday night: “We cannot let this drop. We have to renew the cease-fire, we have to accelerate humanitarian aid and we are going to ask the countries which are the co-sponsors to meet.”

The talks at UN headquarters in Geneva aim to halt a conflict that has allowed for the rise of the Daesh group, sucked in regional and major powers and created the world’s worst refugee crisis.

In an interview with French-language Radio Television Suisse (RTS), de Mistura said 400,000 people had been killed in the war, far higher than the previous UN toll which has varied from 250,000 to 300,000.

The war was tilted in President Bashar Assad’s favor late last year by Russia’s intervention, supported on the ground by members of the Iranian Revolutionary Guard Corps who have been bolstered recently by the arrival of members of Iran’s regular army.

The White House has expressed concern that Russia has repositioned artillery near the disputed city of Aleppo. The Russian military moves have sharpened divisions in Washington over whether President Vladimir Putin genuinely backs the UN-led initiative to end the war or is using the talks to mask renewed military support for Assad.

“The regime is so reliant on external support that it is inconceivable that its allies don’t have the leverage to change its approach,” Britain’s envoy to the Syria peace talks, Gareth Bayley, said on Friday.

Russian Foreign Minister Sergei Lavrov said on Friday that the decision by the opposition High Negotiations Committee (HNC) to quit Geneva was not a loss for anyone except the HNC itself.