United Nations Envoy to Syria Lakhdar Brahimi became the second U.N. representative for the war-torn country to quit in less than two years, signaling a major setback for any negotiated solution to a conflict that has killed more than 150,000 people.

In a press conference at U.N. headquarters in New York Tuesday, Secretary-General Ban Ki-moon said Brahimi would leave his post officially at the end of the month and that the search for a replacement was already underway. Though no official announcement has been made, various reports have speculated that Tunisia’s Foreign Minister Kamel Morjane may take over.

Brahimi’s departure follows the resignation of former Secretary-General Kofi Annan, who quit in August 2012, declaring the situation a “mission impossible.” Brahimi had publicly voiced his frustration with the international community’s inability to work together in the Security Council to end the war in Syria.

Brahimi’s resignation comes just weeks before the Syrian government plans to hold presidential elections on June 3, a vote all but certain to be a sham ending in near-100 percent consensus for President Bashar Assad. The plan for elections underscores the international community’s inability to limit his grip on power, according to Andrew Tabler, a senior fellow in the Program on Arab Politics at the Washington Institute.

“The negotiation settlement in Syria is a very distant reality,” Tabler said. “Assad has successfully waited out another U.N. effort. It’s another blow for the negotiated solution, and it means Assad is free to implement his force.” 

Since taking over from Annan, Brahimi has held two sets of negotiations between members of the opposition and representatives from the regime. Both were unsuccessful.

“I apologize that these two rounds have not come out with very much,” Brahimi said in February in Geneva, following the end of the second round.

Over the past two years, the permanent members of the Security Council have been unable to pass a resolution on Syria that could lead to a peaceful political transition, though the council did pass a resolution to boost humanitarian aid in the country. Russia and China both exercised their veto power on several proposed resolutions. The council needs the assent (or at least abstention) of all the permanent members -- the U.S., France and Great Britain round out the group -- to pass a resolution. 

Brahimi arrived in Iran in March to meet with top officials there about the crisis in Syria. The country had been excluded from the second round of negotiations after members of the Sunni-dominated Syrian opposition said they would boycott if Iran, a Shiite-majority country allied with Assad – who is a member of the Alawite sect, an offshoot of Shi'a Islam -- joined. Experts on the issue have said including Iran in the discussions may be the key to a breakthrough, but according to Tabler that is unlikely given Brahimi’s recent trip to the country and his subsequent resignation.

“I think that there is a possibility we don’t need to start from square one,” he said. “But fighting terrorism is the only (conversation) coming from Assad. As long as he keeps that position I don’t think he is going to go anywhere,” Tabler said, referring to the Syrian president’s claim that the rebels he is fighting are radical Islamists who would turn the country into a haven for jihad on the doorstep of Europe.  

On the ground, Assad's forces have shown no sign of letting up, as the military has launched several attacks in key areas over the past several months. Last week, troops took control of Homs, forcing rebels to evacuate from the city that was their stronghold. According to a Human Rights Watch report released Tuesday, the regime also dropped barrel bombs filled with chlorine gas canisters in the northern part of the country in April.