"No one cares about Annan and his plan," said Ammar Dandash, an anti-government activist in northern Syria who said that no one around him had even remarked on the envoy’s resignation.

Rice, the U.S. ambassador, blamed the failure of diplomacy on both an Assad regime that “continuously broke its pledges” and on unnamed U.N. Security Council members – a reference to Russia and China – that vetoed international sanctions against the Damascus government on three occasions.

“Those members who blocked this action effectively made Mr. Annan’s mission impossible,” Rice said in her statement.

Political analysts, journalists on the ground and Russian allies of Assad all have noted that the opposition camp also failed to implement its side of the Annan-brokered agreement. Opposition forces refused to negotiate while Assad was president, broke the cease-fire first on some occasions and harassed U.N. monitors who were visiting opposition enclaves, according to analysts and news reports.

“The opposition didn’t want anything but the removal of the regime, and the regime didn’t want anything but the removal of the opposition, so Annan was irrelevant from the beginning,” said Azzedine Layachi, a Middle East specialist and professor of government at St. John’s University in New York. “By deciding now that it’s time to leave, he’s trying to save as much as he can of his prestige.”

Already, cartoons have circulated depicting Syria as Annan’s “second Rwanda,” a reference to the African genocide that Annan publicly has said he could’ve done more to prevent during his time as head of U.N. peacekeeping forces in the mid-1990s.

As the fighting has intensified in the last two weeks with sustained rebel offensives in Damascus and Aleppo, civilian and rebel death tolls of more than 100 a day have become common. The Syrian government stopped reporting military and security forces’ deaths in June, when rebels killed at least 649 soldiers, according the government.

Executions have become commonplace, with each side accusing the other of atrocities this week. Residents of southern Damascus said 26 people were executed on Wednesday in Yalda, while rebels posted video of executions of government supporters in Aleppo earlier this week. Heavy shelling and casualties were reported by anti-government activists across the country, including in Damascus.

Allam reported from Washington; Enders, a McClatchy special correspondent, reported from Beirut.