UNITED NATIONS - The United States, its European allies and the UN chief slammed Syrian President Bashar Assad on Monday for a year-long assault on anti-government protests that has killed thousands of civilians and brought Syria to the brink of civil war.The Western powers also urged Russia and China, which have twice vetoed UN Security Council resolutions condemning the Syrian government's attacks on its own citizens, to stop preventing council action against Damascus. Moscow, however, voiced its "grave concern" at the escalating violence Syria, its close ally.A popular uprising against Assad erupted a year ago. The United Nations estimates Syrian security forces have killed well over 7,500 people. Syria said in December that "terrorists" had killed more than 2,000 soldiers and police.US Secretary of State Hillary Clinton blasted Assad for launching new attacks while meeting with Annan to discuss the former UN chief's peace proposals in Damascus at the weekend."How cynical that, even as Assad was receiving former (UN) Secretary-General Kofi Annan, the Syrian Army was conducting a fresh assault on Idlib and continuing its aggression in Hama, Homs, and Rastan," she said.Dozens of civilians in Syria's flashpoint city of Homs were killed in cold blood, the government and opposition said on Monday, disputing responsibility for what both sides called a massacre during a visit from special envoy Kofi Annan."There are grave and appalling reports of atrocities and abuses (in Syria)," Annan told reporters in Ankara before meeting Turkish Prime Minister Tayyip Erdogan. "Killings of civilians must end now. The world must send a clear and united message that this is simply unacceptable."Assad said after meeting Annan on Saturday that dialogue with the opposition would not be successful while "armed terrorist groups" continued to spread instability.Clinton also took a shot at Russia and China, which have demanded that fellow council members balance any condemnations of the violence by the Syrian government with rebukes of the opposition, a position the Western powers refuse to accept."We reject any equivalence between premeditated murders by a government's military machine and the actions of civilians under siege driven to self-defense," Clinton said.Russia voices "concern"Washington and Paris have said that a third draft Security Council resolution urging an end to the violence in Syria and access for humanitarian aid agencies - this time written by the United States - was unlikely to be adopted because of opposition from Moscow and Beijing.Russian Foreign Minister Sergei Lavrov reiterated Moscow's complaints about NATO operations in Libya, where Russia says the alliance went beyond its mandate to protect civilians last year after rebels rose up against the government of Libyan leader Muammar Gaddafi, who was ousted and killed by opposition forces.But Lavrov said Russia shared other countries' worries about Syria, saying it "remains a cause of grave concern for Russia and the whole international community." He said Moscow could support a Security Council resolution along the lines of previous Russian proposals that were unacceptable to Washington and Europe.China did not send its foreign minister to the meeting, but Beijing's UN Ambassador Li Baodong made clear that his country has reservations about council action against Damascus."China is against any interference in internal affairs in the name of humanitarianism," he said.French Foreign Minister Alain Juppe urged Moscow and China to stop preventing the council from taking action on Syria."It is unacceptable that our council should be prevented from shouldering these responsibilities (to the Syrian people)," Juppe told the council. "I call upon China and Russia to take their responsibilities."British Foreign Secretary William Hague, who was presiding over the council meeting in Britain's capacity as Security Council president this month, said the council had not lived up to its responsibility to the people of Syria."The situation in Syria casts a long shadow over this debate," Hague said. "In the eyes of the overwhelming majority of the world, this council has so far failed in its responsibilities towards the Syrian people."Juppe warned Assad that he and his government would face a day of reckoning for "Syrian crimes.""The day will come when perpetrators have to respond to matters being brought against them in the International Criminal Court," he said.Speaking at a special UN Security Council meeting on the "Arab Spring" uprisings across the Middle East and North Africa, UN Secretary-General Ban Ki-moon appealed to Assad to act within the next few days on peace proposals by UN-Arab League envoy Kofi Annan."The Syrian government has failed to fulfill its responsibility to protect its own people and instead has subjected its citizens in several cities to military assault and disproportionate use of force," Ban told the 15-nation council. "These shameful operations continue."