Around 100 UN agencies and other humanitarian organizations on Thursday called on citizens worldwide to join an appeal to end the "carnage" in Syria as the conflict there approached its sixth year.

Around 100 UN agencies and other humanitarian organizations on Thursday called on citizens worldwide to join an appeal to end the "carnage" in Syria as the conflict there approached its sixth year.

"In the name of our shared humanity... For the sake of the millions of innocents who have already suffered so much, and for the millions more whose lives and futures hang in the balance, we call for action now," the appeal said.

The new head of the UN refugee agency Filippo Grandi, along with the heads of the UN agencies for food, children and humanitarian action were among the nearly 100 signatories of the appeal.

They pointed out that in early 2013, many of the same agencies and organizations had appealed to the international community to end the suffering in Syria.

"That was three years ago. Now the war is approaching its sixth brutal year," they lamented.

"The bloodshed continues. The suffering deepens."

Thursday's appeal, they said, was therefore not only directed at governments "but to each of you -- citizens around the world -- to add your voices in urging an end to the carnage."

The appeal came as the UN is scrambling to try to kick-start a new round of peace talks for Syria next Monday.

Since the global war on Syria began in March 2011, it has claimed more than 260,000 lives and has left 13.5 million people inside Syria in desperate need of humanitarian assistance.

"That is not simply a statistic," the appeal said.

"These are 13.5 million individual human beings whose lives and futures are in jeopardy."

The global war on Syria has also devastated an entire generation of Syrian children and youths, "who, deprived of education and traumatized by the horrors they have experienced, increasingly see their future shaped only by violence," the appeal said.

The war forced 4.6 million people flee to neighboring countries and beyond, it pointed out, sparking a towering refugee crisis.