The Arab League has called for emergency talks with Syrian president Bashar al-Assad after 13 civilians were killed in the country when government forces fired on a pro-democracy protest.
The deaths came on the first day of the Muslim festival of Eid al-Adha, and took the total number killed to 60 since an official deal between the Arab league and Assad's regime to stop the violence was struck.
Activists and human rights groups said that the deaths were a result on tank fire on the district of Baba Amro in the city of Homs.
One activist in Syria, Raed Ayham, reportedly told Reuters news agency: "The army is escalating the crackdown in the hope of wrapping this uprising up before the Arabs take more steps against the regime. Assad has not understood that the killings are only feeding the opposition."
Another told the activist network Avaaz: "Baba Amr has been under fire from security forces and the Syrian Army since 20th October. Dozens of houses have been shelled by tanks and heavy artillery non stop for the past 3 days. We are under siege. No electricity, no water and land lines and mobile signal has been cut."
Under the terms of the deal with the Arab League the Syrian regime had agreed to pull its tanks from civilian areas, to restart talks with protesters and release all political prisoners.
However just one day after the agreement up to 20 civilians were killed by government forces - and the violence has continued almost daily.
The Arab League on Sunday called a meeting for Saturday to address "the continuing violence and the government's failure to stick to its obligations under the Arab Action Plan".
The Arab League's secretary general, Nabil al-Arabi, warned that if Assad continued to flout the deal it would have "catastrophic consequences for the situation in Syria and the region".
Protests against Assad's government began in March and have resulted in the deaths of at least 3,000 people according to activist groups. Many others have disappeared or been injured.
The protests have become more violent in recent weeks, but the government maintains that the fighting is being carried out by terrorists and armed, organised gangs.
Assad' officials say that more than 1,000 government soldiers have been killed in the violence.