UN mediator Lakhdar Brahimi apologized to the Syrian people on Saturday after peace talks in Geneva ended without any progress.
He admitted that the talks "had not come out with very much."
The main sticking point was the government’s refusal to talk about a transitional governing body, Brahimi said.
No date has been set for a third round of talks.
Meanwhile, the Syrian Observatory for Human Rights said on Saturday that more than 140,000 people, over 7,000 of them children, have been killed in Syria's uprising-turned-civil war.
The pro-opposition Observatory said the period since the "Geneva 2" peace talks for Syria began last month had been the bloodiest of the nearly three-year conflict.
The death toll is now at 140,041, according to the Observatory, which is based in Britain but has a network of activists across the country. Among the dead were 7,626 children and 5,064 women.
The revolt against President Bashar Assad began as peaceful street protests but transformed into an armed insurgency after a fierce security force crackdown. It has since descended into a civil war with sectarian dimensions.
The Observatory's toll could not be independently verified by Reuters. The United Nations said last month it would stop updating its death count in Syria as dangerous conditions on the ground made estimates impossible to update with accuracy.
The Observatory said all those cases included in its count were those it could document with either names and identification documents, or pictures and videos. It said the fate of tens of thousands more people remained unknown.
The Observatory said it counted more than 30,000 rebels killed and over 50,000 from pro-Assad forces. But the group's chief, Rami Abdelrahman, said the true toll on both sides was likely much higher - by perhaps more than 60,000.
Groups on both sides try to hide their casualties, he said, making fighter death tolls very difficult to gauge.
"The Observatory would like to point out that these statistics do not include the fate of more than 180,000 people missing inside the regime's prisons," it said in a statement.
"Nor does it include more than 7,000 detained by regime forces and armed groups loyal to it, or the hundreds of people kidnapped (by rebel groups) because they are believed to be regime loyalists."
The Observatory called for an immediate ceasefire for the Geneva peace talks, now planned to go into a third round.
"It is shameful that the international community has done nothing to show that it will defend human rights," Abdelrahman told Reuters by telephone. "They are just looking on at this tragedy. The Syrian people dying are just statistics to them."
Also on Saturday, Syria added opposition delegates at peace talks in Geneva to a "terrorist list" and seized their assets, including the house of one of them, anti-government negotiators and a diplomat said on Saturday.
The opposition delegation only learnt of the decision when a copy of the Justice Ministry decision was leaked this week to the opposition website http://www.all4syria.com, the sources said.
The memorandum, issued by the Justice Ministry, says the assets had been frozen under a 2012 anti-terrorism law.
The decision will further antagonize opposition members and their international backers after a second round of negotiations failed on Saturday to achieve any meaningful gains beyond an agreement to meet again at an unspecified date.
One diplomat said the opposition negotiators had discovered a few days ago that most of them were on a "terrorism list" of 1,500 activists and rebels opposed to President Bashar Assad.
Asked why Damascus had put members of the opposition Nation Coalition umbrella group on its terrorism list and frozen their bank accounts, Syrian government delegate Bashar Jaafari said: "You are trying to terrorize me and you won't succeed."
He said the decision was made two months before the Geneva talks began. "This has nothing to do with the Geneva conference. Whoever refuses to fight terrorism is part of terrorism."
Members of the National Coalition make up the bulk of the opposition delegation to the talks, which opened on January 22.
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