Russia and China on Thursday vetoed a UN Security Council resolution on Syria for the third time, sparking outrage by the Western nations which demanded sanctions against President Bashar al-Assad.
The US presidency called the third veto in nine months "highly regrettable". Britain said it was "appalled". France said Russia and China had given the Syrian government time to "crush the opposition."
Eleven of the 15 nations on the council voted for the resolution, Russia and China voted against -- killing the resolution, as permanent members of the council have veto power -- while Pakistan and South Africa abstained.
Amid growing doubts over the future of the peace mission of UN-Arab League envoy Kofi Annan, the United States said it would now act outside of the UN body to confront Assad.
US ambassador Susan Rice called the veto "dangerous and deplorable".
"We will intensify our work with a diverse range of partners outside the Security Council to bring pressure to bear on the Assad regime and to deliver assistance to those in need," she said.
"The Security Council has failed utterly in its most important task on the agenda this year," she added.
"It is clear that Russia only aims to give more time to the Syrian regime to crush the opposition," said France's envoy Gerard Araud.
"Refusing Annan the means of pressure that he asked for is to threaten his mission," Araud told the council.
Britain is "appalled" at the veto, said British ambassador Mark Lyall Grant, whose country took the lead in writing the resolution.
"The effect of their actions is to protect a brutal regime. They have chosen to put their national interests ahead of the lives of millions of Syrians."
The British text, backed by the United States, France, Germany and Portugal, threatened non-military sanctions under Chapter VII of the UN Charter if Assad does not withdraw heavy weapons from Syrian cities.
Russia, Assad's key ally, refused to accept sanctions or action under Chapter VII.
Western nations wanted to use the resolution to justify "external military involvement" in Syria," Russia's UN ambassador Vitaly Churkin said, adding that they sought to "fan the flames" of violence.
China's ambassador Li Baodong said Western nations had been "arrogant and rigid" in negotiations on the resolution. The text would "not only further aggravate the turmoil, but also result in spillover to other countries in the region."
The sanctions proposal was added to a resolution on renewing the UN Supervision Mission in Syria (UNSMIS), whose 90-day mandate ends on Friday.
Without a resolution, the UN may have to hurriedly withdraw the nearly 300 unarmed observers now in Damascus.
The UNSMIS operation has been suspended since June 16 because of the mounting violence.
The Security Council is now scrambling to agree a simple rollover resolution on UNSMIS that could be voted Friday.
More than 17,000 people have been killed since an uprising against Assad began 16 months ago, activists say. The Security Council faces growing criticism over its failure to take action.
Annan said he was "disappointed" at its failure to put united pressure on Assad. UN chief Ban Ki-moon "deeply regrets" the veto, said a spokesman.
Both had earlier called on the Security Council to ensure that there were "consequences" for the failure of Assad and the Syrian opposition to apply Annan's peace plan.
"The hour is grave. The international community has a collective responsibility to the Syrian people," said Ban.
Ban on Thursday ordered his top military advisor, General Babacar Gaye, to Syria to take charge of an observer mission as the UN Security Council wrangled over the future of the operation.