World powers piled pressure on Syria to let in observers as activists reported at least 12 civilians killed by security forces on Saturday's anniversary of International Human Rights Day.
"The world celebrates human rights as human rights are being violated in Syria," the opposition Syrian Revolution 2011 said in a message posted on its Facebook page.
In Oslo, the Nobel Committee head said at the 2011 Peace Prize awards ceremony that this year's award to Yemeni activist Tawakkol Karman served as a warning to dictators in Arab countries such as Syria and Yemen.
"The leaders in Yemen and Syria who murder their people to retain their own power should take note of the following: mankind's quest for freedom and human rights can never stop," Thorbjoern Jagland said.
UN Human Rights Commissioner Navi Pillay has said more than 4,000 people have been killed in a government crackdown on dissent in Syria since the anti-regime protest movement broke out in March.
Pillay is to brief the UN Security Council on Syria and the wider Middle East at a meeting on Monday.
President Bashar al-Assad refuses to let investigators from two UN human rights inquiries enter Syria and is resisting Arab League calls to accept monitors despite being hit by regional sanctions on top of US and EU measures.
An Arab League meeting slated for Saturday to mull a response to Syria which wants the bloc to lift sanctions in return for allowing in observers was postponed until mi-December.
Damascus, which blames "armed terrorist gangs" for the violence, meanwhile appealed to the international community to help it find an "honourable exit" to the crisis and stem the flow of weapons into Syria.
"We are appealing to the outside world and our brothers in the Arab world to help Syria (prevent the) channelling (of) weapons" into the country, foreign ministry spokesman Jihad Makdisi said on Friday, speaking in English.
"If we all work together we can find an honourable exit to the crisis."
The bloodshed, however, continues to claim more lives, with activists reporting more than 50 deaths in less than 48 hours.
The Syrian Observatory for Human Rights said at least 41 civilians, including seven children, were shot dead by security forces on Friday, with Damascus and the central city of Homs suffering the heaviest casualties.
At least 12 civilians were reported killed on Saturday, including four hit when security forces fired live ammunition and tear gas at mourners in Maaret Numan in Idlib province and three others hit by "machinegun fire in Hama."
Activists have called for a civil disobedience campaign from Sunday, the first day of the working week in Syria, with sit-ins, closure of shops and universities, and later a general strike.
The opposition Syrian National Council has warned of a looming bloody final assault on Homs using the pretext of what the regime called a "terrorist" attack Thursday on an oil pipeline.
"The regime (is) paving the way to commit a massacre in order to extinguish the revolution in Homs," said the SNC, a coalition of Assad opponents.
Homs, an important central junction city of 1.6 million residents mainly divided along confessional lines, is a tinderbox of sectarian tensions that the SNC said the regime was trying to exploit.
Witnesses in Homs, already besieged by government troops, have reported a buildup of troops and pro-regime "shabiha" militiamen in armoured vehicles who have set up more than 60 checkpoints, the SNC said.
US State Department spokeswoman Victoria Nuland said that Assad would be responsible for any further deaths.
"There are reports today that the government may be preparing a very serious new assault on the city of Homs in a very large-scale way," said Nuland.
London echoed Washington's concern, with Foreign Office minister Alistair Burt saying: "The Syrian government should immediately withdraw its forces from Homs and exercise restraint."
The French foreign ministry said it was "deeply troubled" by the prospect of a military operation in Homs and warned that "Syrian authorities will be held responsible for any action against the population."