Kofi Annan has resigned as the UN-Arab League special envoy for Syria.
"I have therefore informed the secretary-general of the UN and secretary-general of the Arab League today that I do not intend to continue my mission when my mandate expires at the end of August," Annan said.
UN head Ban Ki-moon said in a statement on August 2 that he "deeply regrets" Annan's decision.
Annan authored a six-point peace plan for Syria which was intended to bring an end to the fighting. The plan was never fully adhered to by either side in Syria and the violence has continued.
There was also no agreement how to approach the problem in the UN.
Annan stressed in his press conference that the Syrian people "desperately need action" but criticized the UN Security Council for "finger pointing and name calling."
"At a time when we need -- when the Syrian people desperately need action -- there continues to be finger-pointing and name-calling in the Security Council," Annan said.
World leaders expressed regret over Annan's resignation.
European Union foreign-policy chief Ashton said Annan's peace plan "remains the best hope for the people of Syria."
She called on the UN and the Arab League to work on the "early appointment of a successor" to continue Annan's work towards a peaceful political transition.
Russian President Vladimir Putin said he regretted Annan's departure, and expressed hope that "the international community's efforts aimed at ending the violence in Syria will continue."
Russian Ambassador to the UN Vitaly Churkin said Russia had always supported Annan's work and hoped Annan's final month in the role "is going to be used as effectively.”
"We regret that he chose to [step down]. We have supported very strongly Kofi Annan's efforts. He has another month to go, and I hope that this month is going to be used as effectively as possible under these very difficult circumstances in order to keep pursuing the goal of a political settlement in Syria and stopping the bloodshed in that country," Churkin said.
However, Ban said the "persistent division" within the UN Security Council had become "an obstacle to diplomacy, making the work of any mediator vastly more difficult."
The UN Security Council has so far failed to agree on what action to take on Syria.
Russia and China have vetoed resolutions on the crisis three times, citing opposition to any action which might be seen as regime change imposed from outside.
Ban said he was discussing with the Arab League whom to select a successor to Annan.
Annan was appointed the joint UN-Arab League envoy in February and charged with finding a way out of the escalating conflict.
Activists say some 20,000 people have died since antigovernment protests erupted in March last year.
Tens of thousands of people have fled Syria.
With reporting by Reuters and AP