Residents of the Zamalka district on the outskirts of Damascus were struggling Sunday to bury dozens of people killed in a horrific attack on a funeral procession Saturday, as diplomats scrambled to resuscitate a plan to end spiraling violence in the country. The source of Saturday’s attack, which killed some 40 people in the city 6 kilometers east of Damascus remained unclear. Activists blamed government forces for the explosion, which they said was likely the result of a car bomb detonated near a mosque where the funeral of an activist killed by regime gunmen was being held. Amateur videos from the scene uploaded to YouTube showed several dozen people, mostly men waving Syrian revolutionary flags and shouting slogans as they accompanied the funeral cortege, when the picture was interrupted by an explosion. Another showed the scene moments later, as a cloud of smoke dissipated to reveal numerous bodies, some with their limbs torn, lying on the ground, as people walked about dazed and disoriented. Activist groups called for urgent assistance to Zamalka Sunday, saying there was not enough medical equipment to treat the wounded, while snipers stationed in the city made it impossible to bury the dead. The attack came during a week of heavy bloodletting in the country. Opposition groups said more than 800 people have been killed this week as Syrian forces pressed ahead with efforts to “cleanse” opposition strongholds. At least 83 people, mostly civilians, were killed Saturday alone, according to the Britain-based Syrian Observatory for Human Rights. Government troops also bombed and shelled other towns across the country Sunday. And in Douma, on the outskirts of Damascus, Syrian forces swept through corpse-strewn streets, after retaking the opposition hub following weeks of relentless shelling. Free Syrian Army fighters fled the town Saturday and residents said they feared a massacre at the hands of troops entering the area. “Douma is completely destroyed,” activist Susan Ahmad told Reuters. “If you go to Douma you can smell the bodies. It’s really like a ghost city.” The Observatory urged the International Committee of the Red Cross and the Syrian Arab Red Crescent to “urgently send medical teams” to the town of Douma. “More than 100 families remain in the town, unable to flee and forced to take refuge in shelters,” it said, adding that most of those trapped were women and children, after the majority of the men had fled repeated arrest sweeps. “Many of the wounded have died because of bad medical conditions,” the Observatory said. The dire reports from the ground came as representatives of global and regional powers met Saturday in an increasingly desperate bid to agree on a peaceful formula to end the bloody crisis in Syria, including Assad’s role in a transitional government. The talks hosted by the United Nations at its European headquarters in Geneva were seen as a last attempt to salvage a peace plan brokered by the U.N.-Arab League envoy Kofi Annan. Annan, a former U.N. secretary-general, said after the Geneva talks the transitional government should include members of Assad’s administration and the Syrian opposition and that it should arrange free elections. He warned at the opening of the meeting that history would not look favorably on leaders who failed to chart a strategy to end the bloodshed. “History is a somber judge – and it will judge us all harshly if we prove incapable of taking the right path today,” Annan told reporters. The meeting agreed that Syria should seek a transitional unity government, but Moscow and Beijing successfully blocked language that would have suggested the new arrangement should exclude Assad. Western officials say the text agreed at the talks still implies indirectly that Assad should stand down, but Moscow said it does no such thing. U.S. Secretary of State Hillary Clinton insisted that Assad would still have to go, saying it is now “incumbent on Russia and China to show Assad the writing on the wall.”Russian Foreign Minister Sergei Lavrov said the Geneva agreement did not imply at all that Assad should step down, as there were no preconditions excluding any group from the proposed national unity government. French Foreign Minister Laurent Fabius said the creation of a unity government implied an end to Assad’s rule, since the opposition would not join unless he left. “The opposition will never agree to him, so it signals implicitly that Assad must go and that he is finished,” Fabius told television station TF1 Sunday. Syrian state media dubbed the meeting a failure. “The agreement of the task force on Syria in Geneva Saturday resembles an enlarged meeting of the U.N. Security Council where the positions of participants remained the same,” reported Al-Baath newspaper. Iran, a strong ally of Assad, echoed that sentiment, saying the Geneva meeting had been “unsuccessful” because Damascus and Tehran were not invited. “This meeting was unsuccessful ... because Syria was not present and some influential nations were not present,” Hossein Amir Abdolahian, an Iranian deputy foreign minister, told state television. Neither Saudi Arabia nor Iran were invited to attend. Syria’s main opposition groups also rejected the plan on the basis that the transition did not bar Assad from participating. Burhan Ghalioun, a senior member and former head of the opposition Syrian National Council, told pan-Arab television Al-Arabiya that “this is the worst international statement yet to emerge from talks on Syria.” Syrian opposition groups plan to meet Monday in Cairo to try to agree on a common vision to deal with the next stage in the conflict, Arab League deputy chief Ahmad ben Heli told reporters. He said the foreign ministers from the five permanent U.N. Security Council members – the United States, Britain, China, France and Russia – were invited, as were Annan and envoys from Iraq, Kuwait, Qatar, Turkey and Tunisia. Attempts in the past weeks to hold a similar meeting at the Arab League’s headquarters in Cairo failed due to differences between opposition groups. Meanwhile, tensions between Turkey and Syria escalated Sunday as Ankara said it scrambled fighter jets after Syrian helicopters flew close to the border, underlining mistrust between the two after the downing of a Turkish plane last month. Prime Minister Recep Tayyip Erdogan insisted Sunday that a jet fighter shot down by Syria last month had been in international airspace, dismissing as untrue a U.S. newspaper report that it had been downed inside Syria. Erdogan waded into the row at a meeting of his AKP party, saying that the Wall Street Journal had “unfortunately published a story which is not true.” The comments follow a report Saturday in the newspaper citing U.S. intelligence that claimed the plane had been “most likely hit by shore-based anti-aircraft guns while it was inside Syrian airspace.” Turkey has repeatedly said its F-4 Phantom warplane had been downed without warning in international airspace on June 22, although it admitted that it had violated Syria’s airspace for a short time and “by mistake.” The Turkish military gave further details in a statement Sunday, saying the plane had been inside Syrian airspace “for about five minutes.” “We see no indication it was shot down by a surface-to-air missile” as Turkey says, an unidentified senior U.S. defense official was quoted as telling the paper. Four F-16 warplanes took off Saturday from Incirlik airbase after Syrian helicopters flew 6.5 km closer to the border, the army said in a statement. Two more F-16 jets scrambled from a base in Batman after one helicopter approached the border south of Mardin province.