DAMASCUS (Web Desk) – Over 400,000 people have been killed throughout the last five years of civil war in Syria, the UN special envoy for Syria has estimated.

Explaining that the death toll was based on his own estimate, Staffan de Mistura said that it was not an official UN statistic. He urged major and regional powers to help salvage a crumbling ceasefire in Syria.

“We had 250,000 as a figure two years ago,” said de Mistura. “Well, two years ago was two years ago.”

The UN no longer keeps track of the death toll due to the inaccessibility of many areas and the complications of navigating conflicting statistics put forward by the Syrian government and armed opposition groups.

Fighting has flared up in many parts of the country as the fragile ceasefire appears to be falling apart, the Aljazeera reported.

Government air strikes killed at least 13 in the eastern countryside of Damascus on Saturday, while air strikes and barrel bombs left several dead and injured in the Bab al-Tariq area of Homs, the UK-based Syrian Observatory for Human Rights reported.

De Mistura also appealed to all involved parties to help revamp negotiations between the government of President Bashar al-Assad and opposition groups. “Yes we do need certainly a new ISSG at ministerial level,” the envoy said, referring to the International Syria Support Group which includes the United States, Russia, the European Union, Iran, Turkey and Arab states.

De Mistura compared the apparently stalled political talks on Syria’s future, the unravelling ceasefire agreement and the still limited humanitarian relief deliveries to the three legs of a table.

“The level of danger to the table made of three legs – and a table of three legs is always fragile by definition – [means that help] is urgently required,” he said.

“When one of them is in difficulty we can make it. When all three of them are finding some difficulty, it’s time to call the ISSG.”

He gave no date or venue for the high-level ISSG.

The envoy said he planned to continue peace talks next week, despite the “worrisome trends on the ground”, adding that he would seek clarity from government negotiators about their interpretation of political transition.

The government, which says the future of President Bashar al-Assad is not up for discussion in Geneva, says that political transition will come in the shape of a national unity government including current officials, opposition and independent figures.

Opposition negotiators have rejected any proposal which leaves Assad in power. They have also accused the government of violating a February “cessation of hostilities” agreement, pointing to air strikes on rebel-held areas which have killed dozens of people this week.