UN Secretary General Ban Ki-moon has urged the Security Council to take "determined measures" to end the war in Syria.
"The Syrian people feel increasingly abandoned by the world as they enter the fifth year of the war that has torn their country apart," Ban said in a statement on Thursday.
The suffering continues "under the eyes of the international community, still divided and incapable of taking collective action to stop the killing and destruction," he said.
"I call upon the Security Council to take determined measures to resolve this crisis and on the way forward."
The Security Council has been divided over how to put Syria back on the road to peace, with Russia blocking moves to punish its ally President Bashar al-Assad in Damascus.
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Ban's appeal for action came as more than 20 rights groups accused the Security Council of "failing Syria" despite three resolutions calling for peace efforts, access for humanitarian aid and the protection of civilians.
A plan by UN peace envoy Staffan de Mistura for a freeze in fighting in the northern city of Aleppo appears to be making little headway, as the death toll mounts.
Last year was the deadliest yet in the war, with at least 76,000 people killed out of more than 210,000 since it began on March 15, 2011 with peaceful demonstrations, inspired by the Arab Spring in Egypt and Tunisia.
More than four million Syrians have fled to neighbouring countries and 7.6 million civilians are displaced within the country as Assad's forces battle opposition rebels and extremists from the Islamic State group.
