The death of a leading Syrian opposition figure who was wounded in a hit-and-run outside his Damascus home has left his allies shaken and appears to have poisoned an already fractious peace process.

Mounir Darwish, 80, was a leading member of Syria's internationally backed opposition movement and a familiar figure at peace talks brokered by the United Nations. He was struck by a car Thursday and died Friday night after surgery on his ankle. Friends who visited him after the operation said he appeared to be recovering well and was looking forward to going home the next day.

The U.N. special envoy for Syria, Staffan de Mistura, called for "those involved to be identified and brought to justice," apparently referring to the hit-and-run and not Darwish's treatment afterward. No official cause of death was announced.

De Mistura said late Saturday that Darwish had stayed in Damascus, rather than seek exile, "as he sought peace and a better future for his country."

The death did not appear to have been mentioned in pro-government media, and a representative of the Information Ministry could not be reached for comment. 

Colleagues said friends and family members who had visited the dissident in the hospital on Friday reported that he had been in good spirits and had been awaiting discharge.

"He even called me to tell me that he'd need to stay in bed for a month but that he was ready to receive any documents I needed him to read," said Firas al-Khalidi, who heads the Cairo section of Syria's political opposition, of which Darwish was a part.

The Cairo bloc is one of three that have signed on to an opposition platform as a way to present a united front at the U.N.-brokered talks in Geneva. The delegates have dropped all preconditions to the peace negotiations, relinquishing from a demand that President Bashar al-Assad step down. 

Darwish had been concerned that the Syrian government was growing increasingly hostile to his activities, Khalidi said. 

"When I called recently to ask about a meeting in Riyadh, he said he didn't want to leave because he was worried," Khalidi said. "He would tell me, 'Be careful, Firas.' "

Six years into Syria's war, a coalition of pro-Assad forces has reestablished control over most of the country, with rebel forces hemmed into pockets of the north and south.

Although hopes for an opposition breakthrough at the negotiating table are low — the two sides do not sit in the same room — Western officials say efforts to unify Syria's opposition would increase pressure on Assad's government. 

"It is about removing the argument that the regime kept on making that it had no opposition to negotiate with," one diplomat said.

Heba Habib in Stockholm contributed to this report.