Foreign Secretary William Hague has warned that prospects for a UN Security Council resolution on Syria are "on a knife edge" as the regime's brutal crackdown continued.
Mr Hague said the situation in the Middle East state was "very serious", amid fears that violence in the north would lead to a mass exodus of refugees.
But he made clear there was no chance of a international military intervention to protect civilians, as has happened in Libya.
Syrian government forces are reported to have moved into the northern town of Jisr al-Shughour with tanks and helicopter gunships in response to unrest.
The regime says it is trying to restore order after 120 security personnel were killed.
The advance has sent another wave of people fleeing towards the Turkish border. Some 4,000 are already said to have crossed into the country.
Mr Hague told Sky News' Murnaghan programme the regime's behaviour was "unacceptable" and there were "many accounts of torture and human rights abuses".
"The main thing we are trying to do is get a resolution from the UN Security Council," he said. "That is much more difficult than in the case of Libya. A country like Russia, for instance, has a much closer relationship with Syria than it has had with Libya in recent years.
"But I do believe it is time for the Security Council to make a clear statement of the kind that we are advocating, calling on the Syrian government to respond to legitimate grievances, to release prisoners of conscience, to open up access to the internet, and to cooperate with the UN High Commissioner on Human Rights."
He added: "The prospects of doing so (securing a resolution) are on a knife edge at the moment."