The UN Security Council has condemned the Syrian government for its deadly crackdown on protesters.
It is the first clear condemnation issued by the Security Council, which includes longstanding allies of Syria such as Russia.
The statement was adopted over the fears of some members that any action could lead to Libya-style intervention.
It comes as the Syrian army attacks Hama, a centre of opposition protest, with reports of much loss of life.
Dozens of people are believed to have been killed in the action against Hama, with residents saying tanks have shot their way into Assi (Orontes) Square, in the centre of the city of 800,000 people.
Human rights groups say at least 140 people have been killed in the Syrian unrest since Sunday, mainly in Hama, adding to a civilian death toll believed to be more than 1,600 since March.
Protesters have vowed to rally every evening during the holy month of Ramadan, after nightly prayers.
Late on Wednesday, there were reports of large demonstrations in several Syrian cities.
Activists told AFP news agency that 50,000 people demonstrated in the eastern city of Deir al-Zour, 20,000 in Duma, north of Damascus, and 40,000 in Homs.
At least four people were killed when troops fired on protesters in Damascus, near the southern city of Deraa, and in the central town of Palmyra.
On Thursday, Syria's Sana news agency said that President Bashar al-Assad had issued a decree authorising a multi-party system, apparently ending decades of monopoly on power by the Baath party.
In Wednesday's statement, the council said it "condemns the widespread violations of human rights and the use of force against civilians by the Syrian authorities".
It says those responsible for the violence should be held accountable.
European members of the 15-nation council had pushed for a strong resolution condemning the Syrian government and calling for a rights inquiry.
The BBC's correspondent at the UN in New York, Barbara Plett, says the statement is weaker than what the European states wanted, but stronger than might have been expected given the opposition from some members to saying anything on Syria.
The statement stressed that the only solution to the crisis was a Syrian-led political process, in effect ruling out outside intervention, says our UN correspondent.
It also called for "an immediate end to all violence and urges all sides to act with utmost restraint, and to refrain from reprisals, including attacks against state institutions."
Observers say the phrase is a concession to Russia and other governments that said they wanted a balanced statement that placed some blame with both sides.
Syria's neighbour, Lebanon, while not blocking the statement, disassociated itself from the text after it was adopted - a procedure last used decades ago.
UN Secretary General Ban Ki-moon said the statement represented "the clear message of the international community" to Mr Assad.
"The world has watched the deteriorating situation in Syria with the most profound concern. But the events of the past few days have been brutally shocking," Mr Ban said.
"Just continuing like this is not sustainable. He cannot and they cannot carry on like this, killing their people."
The BBC's Jim Muir, who is following Syrian events from Lebanon, says there was no recognition or acknowledgement of the statement from state TV or the state news agency.
But the UN move will give heart to protesters, as would any gesture of solidarity or support, our correspondent says.
Anti-government protests began in March, inspired by the successful uprisings in Tunisia and Egypt, and soon spread to many cities across the country.
Mr Assad has promised reforms, and on Thursday reportedly issued a decree allowing multiple parties, one of the main demands of the protest movement.
The government adopted a draft law to this effect on 24 July, but the decree gives it immediate effect.
The Baath party has enjoyed a monopoly on power in a one-party system since 1963.
Mr Assad blames the current violence on "armed criminal gangs" backed by unspecified foreign powers.
Access to events in Syria has been severely restricted for international journalists and it is rarely possible to verify accounts by witnesses and opposition activists.
Activists and residents of Hama said tanks pushed in to the city centre on Wednesday morning, reaching Assi Square.
One resident of the city told the BBC's Damascus correspondent, Lina Sinjab, that he believed a massacre was taking place. He said he had seen piles of bodies in different parts of the city.
There are reports that families trying to flee the city have been shot at to force them to turn back.
Some families who have managed to leave have described the situation as worse than the 1980s, when the late President Hafez Assad, father of the current leader, crushed an uprising, leaving at least 10,000 people dead and the old quarter flattened.
Communication with the city is all but completely cut off, as are water and electricity, correspondents say.