UN chief Ban Ki-moon urged world powers on Wednesday to act "in the name of humanity" against Syria's crackdown on dissent, as a US official likened the Damascus regime to a "dead man walking."
Activists said Syrian forces killed another 21 civilians on a day when the US State Department's special coordinator on Middle East affairs Frederic Hof told US lawmakers that "change is surely coming to Syria."
Ban told reporters in New York that the status quo in Syria -- where security forces on Wednesday reportedly shot dead civilians, cut power lines and conducted raids and arrests -- "cannot go on."
"In the name of humanity, it is time for the international community to act", he said.
He said he had sent a UN Human Rights Council report on President Bashar al-Assad's crackdown to the Security Council, which could increase pressure on it to act against Syria, where crimes against humanity may have been committed.
Washington levelled tough rhetoric against both Assad's regime and Security Council members who have blocked UN action.
"It is difficult to predict how much time they have," Hof said in a hearing on US policy toward Damascus, referring to Assad and his loyalists.
He also said it was vital for UN Security Council efforts to protect Syrians from Assad's security forces, calling on Russia, China and India to stop opposing UN action.
"We ask those governments that are insulating this regime from the will of Syria's citizenry: do not make innocent civilians pay the price for your political calculations," Hof said.
"The international community's duty to the Syrian people transcends power politics."
In October, Russia and China blocked a resolution condemning Assad and Moscow said the West is pursuing an agenda of "regime change" by putting pressure on Damascus but not on armed groups.
Hof said that Moscow must be convinced that its support for Assad "is not only helping to facilitate a humanitarian catastrophe, but it is manifestly not in the interests of the Russian Federation because change is surely coming to Syria."
"Our view is that this regime is the equivalent of dead men walking," Hof told lawmakers.
On the ground, the Britain-based Syrian Observatory for Human Rights said 21 civilians were shot dead by security forces across the country, including 11 in Homs, north of Damascus.
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Other fatalities were reported further south in Homs, in the northwestern province of Idlib and in Damascus province.
Meanwhile, the Observatory said "at least eight soldiers were killed in an ambush on four military jeeps travelling in the village of Al-Asharna on the outskirts of (the central city of) Hama."
Wednesday's ambush on troops was the second such insurgent attack in as many days.
Observatory reports cannot be independently verified as most foreign reporters cannot enter or move freely in Syria.
Wednesday's violence spilled over into neighbouring Lebanon, with 10 people, including a nine-year-old child, wounded in two separate shootings at the border, an official and a medical source said.
Meanwhile, a civil disobedience campaign was observed in parts of Syria, including Hama and Homs, Idlib and Daraa, activists said.
The strike, which began on Sunday, aims to "deprive the regime of the financial means it is using to kill our children."
Meanwhile, Syria's official SANA news agency reported that Iran is to lower import taxes on Syrian goods by 60 percent.
The decision came after two days of talks in Damascus between the co-chiefs of a bilateral economic cooperation commission -- Iran's urban development minister, Ali Nikzad, and Syrian Economy Minister Mohammed Nidal al-Shaar, it said.
Iran's parliament on Tuesday passed a bill for a free trade agreement with Syria in a show of support for Assad's regime.
The Syrian National Council, the opposition's most representative grouping, said on its website it is seeking new means to protect civilians and that it will hold a three-day meeting in Tunis from Friday.
On Tuesday, UN rights chief Navi Pillay estimated that more than 5,000 people have died since protests broke out in mid-March.
Pillay said the new toll includes some 300 children, and recommended the Assad regime's crackdown be referred to the International Criminal Court.
The Arab League has called an emergency meeting of the 22-member bloc's foreign ministers in Cairo on Saturday to respond to Syria's proposal to admit observers in exchange for an end to regional sanctions.
Western nations say they are waiting for the Arab League meeting to decide their next action, with diplomats saying Russia would almost certainly use its Security Council veto again unless there is a strong Arab lead on the crisis.