At least 3,500 people have been killed in Syria since protests against President Bashar al-Assad's government began, the UN has said, as activists report an escalation in brutal attacks on civilians.
Human rights groups said on Tuesday that the city of Hama is being "stormed" by soldiers and tanks.
"The brutal government crackdown on dissent in Syria has so far claimed the lives of more than 3,500 Syrians," a spokeswoman for the Office of the UN High Commissioner for Human Rights, Ravina Shamdasani, said in a statement.
"We are deeply concerned about the situation and by the government's failure to take heed of international and regional calls for an end to the bloodshed."
She added that more than 60 people have been killed since Assad agreed terms for a peace deal in conjunction with the Arab League last week, including 19 on a single day.
Shamdasani said: "Since Syria signed the peace plan sponsored by the League of Arab States last week, more than 60 people are reported to have been killed by military and security forces, including at least 19 on the Sunday that marked Eid al-Adha."
The UN statement follows calls from the Arab League and other nations for Syria to pull its tanks out of civilian areas and stop the violence against citizens - as it had theoretically agreed to do last week.
"The Syrian National Council is calling on the Arab League and the UN to provide protection to the civilians in Homs as a disaster area," a senior Arab League official told CNN.
He said: "They want UN troops on the ground, which would require approval from the UN Security Council and the cooperation of the Syrian government. It is a complicated process yet the support of humanitarian agencies ... may be essential at this stage."
The SNC said that food is running out in some areas, and said that bodies are "rotting in the streets" while calling for an immediate end to violence.
Activists and human rights groups have reported a series of brutal and escalating attacks against civilians in Homs over the past week, with up to 20 civilians being killed in a single day.
The London-based Syria Observatory For Human Rights (SOHR) reported that corpses found in a Homs-area hospital indicated "horrific" marks of torture.
It added that the city of Hama was being "stormed" by Syrian forces, including armoured vehicles.
The SOHR said: "Hama has been... subjected to an extensive security operation by army groups , security forces and Shibiha [thugs]. This was from all directions, and with the usage of armoured vehicles in an attempt to break into the city again.
"Up to now, the boom of explosions, artillery bombardment, and the sounds of heavy and light machine guns are heard everywhere, especially at the western entrance of the city.
"Additionally, there was a heavy weapons firing from Hama’s Castle, downtown the city, and from the polyclinic in Munakh area, specifically the building of Baath Party in the area of Hadir, as well as the building of Positions’ Leadership in Dabagha Street, and also from the military barriers widely spread in the districts of the city.
"There was a movement of the tanks based at the eastern entrance of the city, specifically, the area of Mazarib Bridge. The entering of a number of armoured vehicles to the downtown of the city was noticeable."
British Foreign Secretary William Hague said on Tuesday he was "appalled by the continuing deaths in Syria" and urged Assad's regime to end its siege of the city of Homs.
"It is deplorable that despite making a commitment to the Arab League to end the violence last week, the Syrian government has escalated the repression and many more people have died as a result," he said, and reiterated calls for president Assad to stand down.