It said Ban "appeals to the region and the international community and in particular to the Russian Federation and the United States ... to take clear steps to re-energize the Geneva process," Ban's press office said in a Wednesday statement issued on the third anniversary of the Syrian uprising.

"Syria is now the biggest humanitarian and peace and security crisis facing the world, with violence reaching unthinkable levels," the statement said.

"Syria's neighbors are bearing the increasingly unbearable humanitarian, security, political and socio-economic effects of this conflict."

With the Syrian conflict now entering a fourth year this week and more people fleeing the war, the United Nations has warned that Syrians are about to replace Afghans as the world's largest refugee population.

The opposition Syrian Observatory for Human Rights has said more than 136,000 have been killed since the unrest began in March 2011.

"Hundreds of thousands of lives have been lost or destroyed, with hundreds of people more killed every day," the UN statement said. "Cities and villages have been reduced to rubble; extremists are imposing their radical ideologies; communities are threatened and attacked."

"The secretary-general deeply regrets the inability of the international community, the region and the Syrians themselves to put a stop to this appalling conflict," the UN statement said. "The international community cannot afford to lose focus or look the other way."

Two rounds of peace talks mediated by UN-Arab League peace mediator Lakhdar Brahimi in the Swiss city failed to bring the government and opposition any closer to agreement on a transitional government as called for in a declaration adopted at an international conference in Geneva in June 2012.

NTJ/NJF