Syrian security forces killed six civilians on Tuesday during a raid on anti-government protesters amid reports the United States expects the fall of President Bashar al-Assad and more violence after.
Meanwhile, an activist group inside Syria announced its backing for a recently named National Council of opposition figures, underscoring the need for unity in the campaign to overthrow the regime.
Four civilians were killed in the central city of Homs, including a woman and an 11-year-old boy who died when their bus was fired on, the Britain-based Syrian Observatory for Human Rights said.
Another two died during searches carried out in the Damascus region.
The security forces closed roads into the city, where huge anti-regime protests were staged on Monday.
The demonstrations were dedicated to Zainab Homsi, whose mutilated body was handed to her family by the authorities, the activists said.
And state news agency SANA said the army had deactivated a 25 kilogramme (55 pound) bomb placed near the oil pipeline that feeds the refinery in Homs.
Elsewhere, a policeman was shot dead by unknown attackers in the northwestern Jabal al-Zawiya region, and a civilian wounded on Monday died of his injuries, the Observatory said.
It also reported that according to residents, Kiswe just south of Damascus was cut off by security forces after around 40 vehicles transporting troops entered the town on Monday.
As the killing carried on, the New York Times said the United States was increasingly convinced that Assad's regime would fall and was preparing for a possibly violent aftermath.
The newspaper said Washington was quietly working with Ankara to plan for a post-Assad future that could see Syria's various ethnic groups battle for control of the country, potentially destabilising neighbouring states.
It said that despite calling on Assad to step down, the United States had yet to withdraw its ambassador, Robert Ford, because it viewed him as a vital conduit to the opposition and Syria's disparate ethnic and religious groups.
The Times said intelligence officials and diplomats in the Middle East, Europe and the United States increasingly believed Assad would not be able to quash the months-long revolt against his family's four-decade-long rule.
"There’s a real consensus that he’s beyond the pale and over the edge," the Times quoted a senior official in US President Barack Obama's administration as saying.
"Intelligence services say he’s not coming back."
Assad has deployed tanks and troops in an increasingly violent response to anti-government protests inspired by the Arab Spring, with at least 2,600 people, mostly civilians, killed since March 15, according to UN figures.
Obama was to discuss the Syrian crisis and wider turmoil throughout the Middle East in talks with Turkish Prime Minister Recep Tayyip Erdogan on Tuesday on the sidelines of the UN General Assembly.
On Monday, US Secretary of State Hillary Clinton urged longtime Damascus ally Russia to support a "strong statement" at the UN Security Council over the crackdown.
In her talks with Russian Foreign Minister Sergei Lavrov, Clinton expressed US "interest in seeing the Security Council go on record with a strong statement on Syria," a senior administration official said on condition of anonymity.
Last month, Russia proposed a resolution that would omit Western calls to impose sanctions on Assad's regime for its deadly crackdown.
Meanwhile, the Local Coordination Committees, which have been organising the almost daily protests on the ground, gave their backing to the new Syrian National Council, whose membership was announced at an opposition meeting in Turkey last week.
Despite "reservations" over the way in which it was formed and the forces that comprise it, the LCC said it backs the "national council, which has set as its objective supporting all Syrians, whatever their confession or ethnicity, to overthrow the regime and establish a multi-party, democratic and civil society".
"We support it because we hope to unify the opposition and overcome its divisions," it added, urging "all political groups and revolutionaries to support the national council."