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 blocked a resolution backing an Arab League plan that calls for President Bashar Assad to step down. The double-veto outraged the U.S. and European council members who feared it would embolden the Assad regime.

In an unusual weekend session, 13 members of the council, including the United States, Britain and France, voted in favor of the resolution aimed at stopping the brutal crackdown in Syria that has killed thousands of people since anti-government protests erupted a year ago.

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. Damascus has been a key Russian ally since Soviet times and Moscow has opposed any U.N. call that could be interpreted as advocating military intervention or regime change.

The rare double-veto was issued following days of high-level negotiations aimed at overcoming Russian opposition to the draft resolution. In a true display of diplomatic brinksmanship, the U.S., European nations and the Arab League ultimately decided to call Russia’s bluff on its threats to block the measure despite its overwhelming support among council members. Moscow went ahead and used its veto, bringing Beijing along in support.

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 latest outbreak of violence in Syria.

The urgency was heightened by a weekend 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 the bloodiest episode of the nearly 11-month-old uprising against Assad. The U.N. said in December that more than 5,400 people have been killed since March, but it has been unable to update its count for weeks due to the chaos. Hundreds more have been killed since that tally was announced.

After the vote, U.S. Ambassador Susan Rice, in unusually strong language, said the United States was “disgusted” by the vetoes, accusing Russia and China of aiming to “sell out the Syrian people and shield a craven tyrant.” She said their “intransigence is even more shameful” because Russia continues to supply weapons to Syria.

“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.”

“Any further bloodshed that flows will be on their hands,” she added.

Both President Barack Obama and Secretary of State Hillary Rodham Clinton had urged passage of the resolution earlier Saturday.

U.N. Secretary-General Ban Ki-moon expressed “deep regret” over the council’s inability to reach consensus, calling it “a great disappointment to the people of Syria and the Middle East, and to all supporters of democracy and human rights,” his spokesman Martin Nesirky said.

The Security Council’s failure to pass the measure “undermines the role of the United Nations and the international community” in its efforts to end the violence in Syria, he said.

British Ambassador Mark Lyall Grant said his country was “appalled” by the double veto, but would continue efforts to get the Security Council to take action.

“Despite this veto, we will continue as the United Kingdom to strongly support the Arab League plan and we will bring this issue back to the Security Council if the Syrian regime does not end the bloodshed and implement the plan as has been demanded,” Lyall Grant said.

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 the draft remains on the table and hoped that consensus can still be reached to take another vote later.

Russian Ambassador Vitaly Churkin told reporters afterward that he was encouraged by statements about “the intention to continue diplomatic efforts” and noted that the Security Council is “not the only diplomatic tool on the planet.”

Churkin said that Russian Foreign Minister Sergey Lavrov and the country’s foreign intelligence chief, Mikhail Fradkov, will meet with Assad in Damascus on Tuesday, without providing specifics on the purpose of that trip.

The latest U.N. resolution repeated all the conditions that Arab League foreign ministers had set in a Jan. 22 decision on Syria, calling for Assad to delegate his powers to a deputy as part of a Syrian-led political transition to a democratic state.

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, Churkin accused fellow council members of being inflexible by backing what he called an “unbalanced” resolution that failed to contain measures against armed anti-government groups.

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.”

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.

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 Security Council to stand up against the Syrian regime, saying Assad had displayed “disdain for human life and dignity” following the weekend attacks in Homs.

“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.

“Assad has no right to lead Syria, and has lost all legitimacy with his people and the international community,” Obama said.

To the Syrian people, Obama pledged U.S. support and vowed to work with them to build a better future in their country.

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 vetoes.

“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.”

Portuguese Ambassador Jose Filipe Moraes Cabral asked: “How many more dead and maimed will it take for this council to react?”

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.”