UNITED NATIONS -- As Syria marks a grim milestone -- four years of civil strife where 220,000 people have died in a war of documented atrocities -- several organizations are issuing pleas calling on world leaders to stop the fighting.

Millions of people have fled the country and millions more are internally displaced, according to studies, as diplomatic efforts over four years at the UN in New York, Geneva, Damascus and Moscow so far have proved virtually worthless against the pace of the carnage, experts said.

"One runs out of words to harness that which can reveal the depth of suffering and how appalling the lack of a Security Council response is," said Simon Adams, executive director of the Global Centre for the Responsibility to Protect, at the Graduate Center of the City University of New York.

More storiesConflict in Syria: Complete coverage

Adams' group issued a letter and a report, Failure to Protect: Syria and the UN Security Council, which documents inertia at the Security Council, where China and Russia vetoed measures some observers say would have eased the crisis.

Diplomats assignedThe UN itself has tasked three veteran diplomats to end the war -- including former UN Secretary-General Kofi Annan -- and convened international conferences that have yielded no peace.

"The Security Council has in the past shown its ability to act against the use of chemical weapons in Syria and to compel the delivery of humanitarian assistance to vulnerable Syrians," said UN Secretary-General Ban Ki-moon. "I call upon the Security Council to take determined measures to resolve this crisis."

The Centre's letter was distributed to ambassadors and other diplomats, Adams said.

It echoed some of the world's best-known humanitarian organizations, whose leaders also issued a dire warning on the lack of diplomatic success in Syria and used Twitter hashtag #WhatDoesItTake to get the word out.

"We need world leaders to put aside their differences and use their influence to bring about meaningful change in Syria," read the statement signed by UN humanitarian leaders including the Office for the Coordination of Humanitarian Affairs and UNICEF. "To press the parties to end indiscriminate attacks on civilians; to secure the lifting of sieges where more than 212,000 people have been trapped without food for months; to enable delivery of vital surgical and other medical supplies; to end the collective punishment of civilians by cutting off water and power supplies."

advertisement | advertise on newsday

Widespread protestsThe civil war in Syria began in March 2011 amid the Arab Spring that swept longtime strongmen in the Middle East from power after massive protests.

Leaders in Tunisia, Libya and Egypt were toppled or fled. But in Syria, the protests that began in Dara'a were met with a government military crackdown, experts have said, leading to an armed response by rebel and extremist groups -- such as Islamic State and al-Qaida.

UN and independent reports by organizations such as the Syrian Network for Human Rights, the Syrian Observatory for Human Rights and Human Rights Watch document horrific incidents of torture and illegal warfare by both rebels and government forces. The UN Independent International Commission of Inquiry on Syria has said both sides have committed war crimes and crimes against humanity.