Making the announcement during the daily press briefing at UN Headquarters in New York, Mr. Ban said the veteran diplomat would relinquish his post as of 31 May. With the conflict grinding on and no end in sight, Mr. Ban lamented that the lack of a peaceful resolution during the envoy’s tenure was a “tragedy for the Syrian people” and a “failure” for the United Nations.

Appointed on 17 August 2012, Mr. Brahimi took over the peace-facilitation role played by former UN Secretary-General Kofi Annan. A long-time Special Advisor to the UN Secretary-General, Mr. Brahimi was also the former Head of the UN Assistance Mission in Afghanistan (UNAMA) from October 2001 to December 2004.

Mr. Brahimi, present at the briefing, said he was “very, very sad to leave Syria in such a bad state.” Yet, he had no doubt the Secretary-General would do “everything humanly possible” to work with the UN Security Council, the Syrian parties and with neighbouring countries, to end the crisis.

“I’m sure the crisis will end, but all [stakeholders] should consider how much more death, how much more destruction will occur…before Syria can become a new Syria,” said Mr. Brahimi.

In his remarks, Mr. Ban said that for nearly two years, Mr. Brahimi had sought an end to the brutal and still worsening civil war in Syria. Indeed, the 80-year old Algerian diplomat has faced almost impossible odds, “with a Syrian nation, Middle Easters region and wider international community that have been hopelessly divided in their approaches to ending the conflict.”

The conflict in Syria, which began in March 2011, has led to well over 100,000 deaths, and more than 680,000 people have been injured. More than 9.3 million people are in need of assistance inside Syria, including at least 6.5 million who are internally displaced. The conflict has also spawned a refugee crisis in which nearly 2.5 million people have are being sheltered in neighbouring countries.

The Secretary-General said Mr. Brahimi has long been recognized as one of the world's most brilliant diplomats, as well as an outstanding proponent of the principles and Charter of the United Nations.

“That the objective to which he applied his extraordinary talents has proven elusive is a tragedy for the Syrian people,” lamented Mr. Ban, who added: “That his efforts have not received effective support from the United Nations body that is charged with upholding peace and security, and from countries with influence on the Syria situation, is a failure of all of us.”

“He has persevered, with great patience and skill, because he knows that without efforts towards a new Syria, the Syrian people will be condemned to further suffering,” the Secretary-General said.

The UN chief expressed great appreciation for Mr. Brahimi's diplomacy in organizing the Geneva Conference on Syria and for facilitating the intra-Syria talks earlier this year. Those two rounds of talks, the first in January followed by a second round in February, saw both the Syrian Government and opposition representatives sticking to their positions, and yielded only modest cooperation on a humanitarian issue related to aid access in the long-besieged Old City of Homs.

The basis of the talks is full implementation of an action plan adopted in the so-called Geneva Communiqué of 2012, the first international conference on the conflict, which calls for a transitional government to lead to free and fair elections.

“I regret that the parties, and especially the Government, have proven so reluctant to take advantage of that opportunity to end the country's profound misery,” said Mr. Ban, renewing his appeal to them to show the wisdom and sense of responsibility that could allow a way out of this nightmare.

“I also reiterate my strong view that there must be accountability for the terrible crimes that have been - and are being – committed,” he said, underscoring that such crimes include the deliberate starvation of communities by preventing humanitarian access.

The Secretary-General said that he will continue to count Mr. Brahimi’s wisdom, advice and unique experience on other issues of concern to the United Nations. “But that is for tomorrow; he now deserves some rest,” said Mr. Ban.

Responding to questions, the UN chief said that he would continue consultations on the way forward and would make a decision later on Mr. Brahimi’s successor.

“Today, I urge all involved, including those States with influence over the parties, to reflect deeply on what we should do at this moment to generate hope of a better future for the people of Syria,” he said.

“We thought we would be able to deliver but because of a divided world [and] region we have not been able to make any progress. Many people have been killed and displaced,” said Mr. Ban, noting that while there had been some progress regarding humanitarian issues and on the removal and destruction of chemical weapon stocks, there had been no real political progress.