Syria's main political opposition group has formed a military bureau to unify armed resistance to the government.
The Syrian National Council (SNC) said the bureau would bring armed groups under a central command and control the flow of weapons to avoid "chaos".
The government launched a ground assault in the city of Homs this week after weeks of shelling.
The UN's rights council has passed a resolution condemning "systematic violations" against civilians.
The motion, supported by 37 nations, called for the regime to allow access for aid agencies, and demanded an immediate halt to the violence.
China and Russia, which have both vetoed UN resolutions on Syria, voted against the proposal. Cuba also rejected the motion.
The vote carries no legal weight, but analysts say it may embolden diplomats to take a tougher line in UN Security Council debates.
SNC leader Burhan Ghalioun announced the new military bureau at a news conference in Paris.
He said the uprising had begun as a non-violent movement, but the council had to "shoulder its responsibilities in light of this new reality".
Mr Ghalioun said the bureau would function like a defence ministry and be staffed by soldiers from the main armed group, the Free Syrian Army (FSA), as well as civilians.
It would control the supply of arms, track and organise armed groups, manage funding and seek guidance from foreign experts, he said, insisting its function was only to protect peaceful protesters.
Mr Ghalioun said the FSA had agreed to the new organisation.
However, the head of the FSA, Col Riyad al-Assad, has declared his organisation will not co-operate with the new bureau, says the BBC's Jim Muir, in neighbouring Lebanon.
It is extraordinary, our correspondent explains, because the announcement specifically mentioned that the bureau was being established in order to provide arms to the FSA, as well as political control.
What Col Assad is saying is that the FSA does not want any political interference and has its own military strategy, which is to keep fighting the government, our correspondent says.
In other developments:
- Foreign ministers of the six Gulf Arab states have said they will meet Russian Foreign Minister Sergei Lavrov next week to "express disappointment with the Russian stance", according to the AFP news agency
- UN-Arab League peace envoy Kofi Annan has called for unity behind a single mediation effort
- Britain has confirmed it is withdrawing its remaining diplomatic staff from Damascus because of security concerns
- Syria has responded to criticism that it refused to allow UN rights official Valerie Amos into the country, saying she had requested "an unsuitable time", and promising to continue consultations.
The Baba Amr district, where many opposition fighters are believed to be sheltering, has been under bombardment for almost a month.
Many of the area's estimated 100,000 residents have fled to escape the siege, and it is unclear how many are still trapped.
Ground troops moved into the besieged quarter earlier this week, and state TV broadcast footage of smashed and empty streets with the sound of gunfire reverberating.
Communication with the area has been largely cut off, and people are struggling to get in or out.
Government officials claimed to have taken control of Baba Amr late on Wednesday, and said troops were now "mopping up" pockets of resistance.
But opposition activists strongly denied those claims, saying fighters from the Free Syrian Army had managed to push back regime forces.
"They've been trying to enter the neighbourhood of Baba Amr but the Free Syrian Army is fighting back," one activist said.
"It's just miserable here in Baba Amr."
Witnesses in Homs said the city had been blanketed in snow, which has slowed the military assault.
But the cold weather is making life difficult for residents, many of whom are without power and running low on basic supplies.
One resident told the BBC how people were trying to melt snow because they had no water.
Several Western journalists trapped in the latest bombardment in Homs have managed to escape to neighbouring Lebanon in recent days.
But two French journalists, Edith Bouvier, who is seriously wounded, and William Daniels, remain unaccounted for.
Activists say more than 7,500 people have died since the uprising against Mr Assad's government began last March.
The government, however, says at least 1,345 members of the security forces have been killed combating "armed gangs and terrorists", and puts the number of civilians killed at 2,493.