Kofi Annan resigned as UN-Arab League envoy for Syria on Thursday, complaining the international community had not done enough to support his bid to persuade Bashar al-Assad to accept a peace plan.
"I did not receive all the support that the cause deserved," Annan told reporters at his headquarters in Geneva, plunging international peace efforts into limbo even as fierce fighting raged on in Syrian cities.
Annan complained added that "continuous finger-pointing and name-calling" in the UN Security Council had hindered his attempts to implement his so-called "six point peace plan."
"The increasing militarization on the ground and the lack of unanimity in the Security Council fundamentally changed my role," he said.
But he predicted that Syria's President Assad would leave office "sooner or later" and did not rule out his successor having more success.
"The world is full of crazy people like me so don't be surprised if someone else arrives to take it on," he said.
Earlier, UN Secretary General Ban Ki-moon had announced "with deep regret", that Annan had tendered his resignation from the mission and said "divisions" within the major powers had become an obstacle to Annan's efforts.
Annan said that his eventual successor might have more luck in persuading the parties to the Syrian conflict – Assad's authoritarian regime and an increasingly determined armed opposition – to lay down their arms.
But he complained the "disunity of the international community" meant he was unable to put enough pressure on the combatants to follow his six-point plan, which calls for a ceasefire and a negotiated transition of power.
"I am still concerned for the Syrian people. They can still be saved. The men women and children who have already suffered far too much," he said.
Annan denied he had left the Syrian people to fend for themselves, saying: "It means there has to be a shift in attitudes. We need a well-balanced political settlement to resolve this. There is no military solution."
In February, with the Syrian conflict fast degenerating into civil war, the UN and Arab League named Annan, a Nobel Peace prize-winning former UN secretary general, as their joint envoy.
The Syrian president agreed to a six-point peace plan with Annan but he ever carried through with his promises, and the conflict has instead become even bloodier, with shelling in cities and allegations of massacres.
"I wish to express my deepest gratitude to Mr. Annan for the determined and courageous efforts he has made as the joint special envoy for Syria," Ban said in a statement.
"Kofi Annan deserves our profound admiration for the selfless way in which he has put his formidable skills and prestige to this most difficult and potentially thankless of assignments," Ban added.
Annan's mandate will not be renewed when it expires on August 31. Ban said that he is in discussions with the Arab League on naming a successor.
Annan went to Damascus three times for talks with Assad and to press the leader to embark upon a peace process by withdrawing heavy weapons from cities and taking the first steps toward political dialogue.
The special envoy asked the international community to impose "consequences" for not carrying out the peace plan but, according to officials close to him, feels that he did not get the necessary support.
Russia and China three times vetoed UN Security Council resolution which could have led to sanctions against Assad.
Annan's resignation could lead to new quarrelling among the major powers over who is to blame for letting the conflict deteriorate.
Syrian activists say more than 20,000 people have died since the uprising against Assad started in March 2011.
Russia, Assad's key ally and international protector, insisted it had always given strong support to Annan and his peace plan.
"We understand that that's his decision, we regret that he chose to do so," Russia's UN Ambassador Vitaly Churkin told reporters in New York.
"We have supported very strongly Kofi Annan's efforts," Churkin said adding that Annan's final weeks in his post should be used "effectively" to press any lingering hopes of a political settlement.
He acknowledged however that it was a "daunting task."
Asked about Russia's veto, Churkin said: "I have regrets that some council members chose to try to push their agenda through the council." Russia has accused Western nations on the council of only seeking regime change in Syria.
The UN leader said that the Security Council had failed to help Annan.
"Tragically, the spiral of violence in Syria is continuing. The hand extended to turn away from violence in favor of dialogue and diplomacy – as spelled out in the six point plan – has not been not taken, even though it still remains the best hope for the people of Syria," Ban said.
"Both the government and the opposition forces continue to demonstrate their determination to rely on ever-increasing violence. In addition, the persistent divisions within the Security Council have themselves become an obstacle to diplomacy, making the work of any mediator vastly more difficult," Ban said.
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