Democracy activists on Tuesday denounced as "unprofessional" an Arab League observer mission in Syria after the bloc's chief admitted snipers remained active in the country despite their presence.
Echoing concerns over the relentless violence, the White House condemned the brutal treatment of protesters, saying it was "past time" for the UN Security Council to act against Damascus.
And French President Nicolas Sarkozy demanded his Syrian counterpart Bashar al-Assad step down for overseeing "disgusting" massacres of his own people.
The Arab League mission has been mired in controversy since the first observers arrived on December 26, with activists accusing Syria's regime of keeping the monitors on a short leash as it presses on with its lethal crackdown on dissent.
The Syrian Observatory for Human Rights said security forces killed three civilians in the central city of Homs, even as state television reported observers were in the Homs region.
The group also reported two more civilian deaths in Hama, and said 18 members of the security services had died during clashes with army deserters in the southern city of Daraa.
Arab League chief Nabil al-Arabi, in his first remarks since the observers arrived, defended the mission, saying it had secured the release of political prisoners and the withdrawal of tanks from cities.
However, "there are still snipers and gunfire. There must be a total halt to the gunfire," he told reporters on Monday.
The issue would be raised with Syria's government "because the aim is to stop the shooting and protect civilians," Arabi said, adding that "it is difficult to say who is firing on whom".
Arab foreign ministers were to meet in Cairo on Saturday to discuss the mission's first report, the League said on a day when observers faced scathing criticism from activists.
"We want to tell Nabil al-Arabi that the lack of professionalism of the observers and non-compliance with their arrival times in specific places have left many people killed," said the Local Coordination Committees, which organise the protests.
It further claimed the observers were being hampered by the regime.
"Soldiers wear police uniforms, drive repainted military vehicles and change the names of places, but this does not mean the army withdrew from cities and streets, or that the regime is applying the provisions of the Arab protocol."
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The LCC estimate that at least 390 people have been killed since the observers began their mission.
The mission has also been criticised by Syrian activists and opposition figures over the choice of a former top Sudanese military commander, General Mohammed Ahmed Mustafa al-Dabi, to head its observer operation.
Dabi served under Sudan's President Omar al-Bashir, who is wanted by the International Criminal Court for alleged war crimes.
White House spokesman Jay Carney said that "as sniper fire, torture, and murder in Syria continue, it is clear that the requirements of the Arab League protocol have not been met".
"We believe it's past time for the Security Council to act," Carney said. "We want to see the international community stand together united in support of the legitimate aspirations of the Syrian people.
"We're working with our international partners to increase the pressure on the Assad regime to cease the completely unacceptable violence that it's been perpetrating on its own citizens."
The French president said Syrians should be allowed "to freely choose their own destiny" after facing what he denounced as brutal persecution that inspires "disgust and revulsion".
But Algeria expressed optimism about the Arab mission, with Foreign Minister Mourad Medelci saying it would evaluate the situation "in a more credible manner".
And opposition Syrian National Council leader Burhan Ghaliun met the prime minister of Portugal, a current member of the Security Council, and said the observer mission "remains useful even if it does not lead to the implementation of the Arab plan".
"It remains politically, morally and psychologically useful," he said.
But the unity in opposition ranks which Western governments say is vital for a new and democratic Syria remained elusive on Tuesday with the SNC saying that a deal signed on Friday with a rival grouping -- the National Coordination Body for Democratic Change in Syria -- had unravelled.
"This document conflicts with the SNC's political programme and with the demands of the Syrian revolution," the grouping said on its Facebook page.
Widely regarded as the most inclusive of Syria's opposition alliances, with representation from both the Muslim Brotherhood and parties drawn from the Christian and Kurdish minorities, the SNC has been at odds with some activists over the extent of foreign intervention required to bring change.