The United Nations peace envoy for Syria threw in the towel on Tuesday after failing to start a meaningful dialogue, as France accused Damascus of continuing to use chemical weapons.
In a double blow to the already frozen peace process, Lakhdar Brahimi announced his resignation at UN headquarters as French Foreign Minister Laurent Fabius spoke in Washington.
Fabius accused Bashar al-Assad's regime of resorting to banned chemical weapons 14 times in recent months, despite having agreed to hand-over its deadly stockpile to international monitors.
"How much more destruction is there going to be before Syria becomes again the Syria we have known?" Brahimi asked as he confirmed weeks of rumors that he was stepping down.
Brahimi, who took over from the previous UN peace envoy in August 2012, said it was "very sad that I leave this position and leave Syria behind in such a bad state."
Asked what his message for Syrians would be, Brahimi said: "apologies, once more, that we have not been able to help them as much as they deserve; and, tell them the tragedy in their country shall be solved."
The veteran Algerian diplomat, backed by the US and Western allies, had coaxed Assad and Syria's fractious opposition to attend peace talks in Geneva earlier this year.
But negotiations broke down after only two rounds amid bitter recriminations. Meanwhile, the war slipped into a fourth year with an estimated 150,000 dead and millions of refugees.
"He has faced almost impossible odds," Ban said of his 80-year-old envoy, promising to replace him.
Ban blamed the failure to find peace on "a Syrian nation, Middle Eastern region and wider international community that have been hopelessly divided in their approaches to ending the conflict."
Separately, Fabius told reporters in Washington that the 14 reported incidents showed that "in recent weeks, new, smaller quantities of chemical arms have been used, mainly chlorine."
A UN watchdog, the Organization for the Prohibition of Chemical Weapons (OPCW), which is overseeing the removal of Syria's toxic arms, has sent a mission into the war-torn country to investigate.
France and other Western nations are currently examining the evidence with the results expected in a few weeks.
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- France 'regrets' Obama U-turn -
Fabius complained that President Barack Obama had failed to carry out threatened strikes against the Syrian regime last year after a sarin gas attack near Damascus killed hundreds of people.
"We regret it, because we think it would have changed lots of things ... but what is done is done, and we're not going to rewrite history," Fabius told reporters.
But a senior US administration official dismissed the criticism, pointing out that -- without airstrikes -- 92 percent of Assad's stockpile has been destroyed by the OPCW in past months.
"There is no evidence that a strike would have allowed us to remove that amount of chemical weapons," the official said.
Citing witnesses and medical staff, Human Rights Watch said Tuesday it has evidence that "strongly suggests" the Syrian government used chlorine gas on three towns in mid-April.
It documented attacks on the towns of Kafr Zita in central Hama on April 11 and 18, Al-Temana in Idlib on April 13 and 18 and Telmans also in Idlib province on April 21. All are areas under rebel control.
"Evidence strongly suggests that Syrian government helicopters dropped barrel bombs embedded with cylinders of chlorine gas on three towns in northern Syria in mid-April 2014," HRW said.
Syrian opposition leader Ahmad Jarba met with Obama during a planned meeting with National Security Advisor Susan Rice as part of an eight-day trip to the United States, seeking to persuade the White House to drop its reluctance to supply the rebels with heavy arms.
Jarba has specifically called for anti-aircraft missiles in order to be able to combat what he has called "the nightmare" of daily barrel bombings.
Jarba is also likely to attend a meeting of the "Friends of Syria" in London on Thursday, in which US Secretary of State John Kerry and Fabius will also participate.
Syrian opposition UN representative Najib Ghadbian said that the rebels share Brahimi's "frustration with the Assad regime for not engaging constructively in the political process."
Forcing Assad to negotiate "will require concerted international pressure that has so far been lacking," he added.