UNITED NATIONS (AP) - The U.N. Security Council failed again Saturday to take decisive action to stop the escalating violence in Syria as Russia and China vetoed a resolution backing an Arab League plan that calls for President Bashar Assad to step down. The other 13 members of the council, including the United States, Britain and France, voted in an unusual weekend session in favor of the resolution aimed at stopping the ongoing violence in Syria. It was the second time in four months that Russia and China used their veto power to block a Security Council resolution condemning the violence in Syria. The rare double-veto was issued following days of negotiations aimed at overcoming Russian opposition to the draft resolution. Several European envoys said before the session that they felt compelled to call for the vote despite Russia's attempts to seek a delay because they were concerned about the escalating violence by Assad's regime. The urgency was heightened by an assault by Syrian forces firing mortars and artillery on the city of Homs. Activists said more than 200 people were killed in what they called one of the bloodiest episodes of the uprising against Assad. The U.N. says more than 5,400 people have been killed over almost 11 months in a government crackdown on civilian protests. After the vote, U.S. Ambassador Susan Rice, in unusually strong language, said the United States was"disgusted" by the outcome of the vote. "For months this council has been held hostage by a couple of members," Rice said. These members stand behind empty arguments and individual interests while delaying and seeking to strip bare any text that would pressure Assad to change his actions. "This intransigence is even more shameful when you consider that at least one of these members continues to deliver weapons to Assad," she added, referring to Russia, a major arms supplier for Syria. Both President Barack Obama and Secretary of State Hillary Rodham Clinton had urged passage of the resolution earlier Saturday. Moroccan Ambassador Mohammed Loulichki, a key sponsor of the resolution, told reporters afterward that his country was "frustrated and sad" over the outcome. He said that the draft remains on the table and hopes that consensus can still be reached to take another vote later. The latest U.N. resolution repeated all the conditions that Arab League foreign ministers set in a Jan. 22 decision on Syria, calling for a Syrian-led political transition in which Assad would delegate his powers to a deputy. Russia had expressed concerns about the draft text, saying it feared the resolution would lead to the kind of military intervention and regime change seen in Libya after last year's council action intended to protect civilians from attacks by forces loyal to strongman Moammar Gadhafi. After Saturday's vote, Russian Ambassador Vitaly Churkin accused fellow council members of being inflexible. "We greatly regret this result of our joint work" on the resolution, he said. Churkin said his country's proposed amendments to the resolution had been ignored, and the version voted on Saturday "did not adequately reflect the real state of affairs in Syria." Russian Foreign Minister Sergey Lavrov had warned earlier that Moscow would use its veto power if the amendments were not included in the draft text. Russia's proposed changes were aimed at satisfying Moscow's concerns that the resolution made too few demands of anti-government armed groups, and that the text could prejudge the outcome of a national dialogue among political forces in Syria. Lavrov was quoted by Russian news agencies as saying that he and Russia's foreign intelligence chief, Mikhail Fradkov, will meet with Assad in Damascus on Tuesday. Chinese Ambassador Li Baodong said his country joined Russia in voting against the resolution because the proposed amendments were not taken into account. U.S. Ambassador Rice had described those amendments as "unacceptable" as she headed into Saturday's session. Before the vote, Obama had urged the council to take a stand against Assad's regime and back the resolution. "The international community must work to protect the Syrian people from this abhorrent brutality," Obama said in a blistering statement issued by the White House. Obama said Assad had displayed "disdain for human life and dignity" following the weekend attacks in Homs. Clinton met Saturday with Lavrov on the sidelines of a security conference in Munich, Germany, to urge immediate U.N. action on Syria, but was unable to dissuade Russia from wielding its veto power as a permanent council member. Other council members joined the U.S. in condemning the veto. "It is a sad day for this council, a sad day for Syrians and a sad day for all friends of democracy," French Ambassador Gerard Araud said after the vote. Araud said Russia and China had "made themselves complicit in a policy of repression carried out by the Assad regime." British Ambassador Mark Lyall Grant said his country was "appalled" by the double veto and accused Russia and China of "turning their backs" on Arab nations. Portuguese Ambassador Jose Filipe Moraes Cabral bemoaned members' inability to reach consensus, and asked: "How many more dead and maimed will it take for this council to react?" "Today the Security Council has failed to live up to its responsibility," German Ambassador Peter Wittig said. The people in Syria have been let down again. Human rights advocates feared that the resolution's failure might encourage the Assad government to intensify its violent crackdown on anti-government protesters. "The risk is high that the Assad regime will see this double veto as a green light for even more violence," said Philippe Bolopion, who monitors the United Nations for Human Rights Watch. Vetoes by Russia and China are not only a slap in the face of the Arab League, they are also a betrayal of the Syrian people. Associated Press writers Matthew Lee and Geir Molson in Munich and Vladimir Isachenkov in Moscow contributed to this report.