Syrian forces shot dead at least 19 civilians on Sunday in a continued military assault on the restive city of Homs and in attacks on pro-democracy demonstrations that erupted after prayers marking the main Muslim feast, activists said.
Qatar's prime minister called for Arab states to meet next Saturday to weigh Syria's failure to implement a deal struck with the Arab League to end bloodshed that was touched off by the popular uprising against President Bashar al-Assad.
The Egyptian official news agency MENA said the gathering would address "the continuing violence and the government's failure to stick to its obligations under the Arab Action Plan to solve the crisis in Syria."
Arab leaders have ramped up criticism of President Assad as the killings mounted, but have shied from demanding major political change in the country for fear chaos could ensue, given Syria's volatile sectarian divisions. Syria is dominated by Mr. Assad's minority Alawite sect while Sunni Muslims form the majority.
Damascus has described increasing Arab criticism as unproductive and based on false media reports.
It says the unrest has arisen largely from a foreign conspiracy to divide Syria and that security forces are using legitimate means to confront "terrorists" and Islamist militants bent on wrecking a reform drive by Mr. Assad.
Opposition leaders say the protests are driven by broad discontent with a corrupt repressive elite, not by violent extremists, and that Mr. Assad's promises of reform have been discredited by his continuing military crackdown on protesters.
In an address to Syrians aired live on al-Jazeera television, prominent opposition figure Burhan Ghalioun said the Syrian National Council, formed in Istanbul two months ago, has asked the Arab League and United Nations to help protect Syrian civilians by sending in international human rights monitors.
Most of the deaths on Sunday occurred in Homs, 140 kilometres north of Damascus, where a main district has been under tank bombardment since the day before Syrian authorities agreed in Cairo to the Arab League initiative last Wednesday.
Under the deal, the army was supposed to pull out of turbulent cities, political prisoners would go free and talks with the opposition would begin within two weeks.
Troops and militiamen loyal to Mr. Assad deployed in several Damascus suburbs on Sunday, surrounding mosques to prevent crowds from rallying after the morning prayers for the feast of Eid al-Adha.
"There is disillusionment that the Arab League agreement has failed to curb the repression," local activist Raed Ayham told Reuters by phone. "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 against him."
Syrian authorities have banned most non-official media since the revolt against 41 years of rule by the Assad family and their Baath Party erupted in March, making independent verification of events difficult.
Authorities say Islamist militants and foreign-backed armed gangs have killed 1,100 members of the security forces during the uprising. The United Nations says more than 3,000 people have been killed in Assad's crackdown.
In Cairo on Saturday, the head of the Arab League said it was seriously concerned by the violence in Syria, and appealed to Damascus to abide by steps agreed with Arab states to protect civilians and set Syria on a course of political dialogue.
Western leaders have called for Mr. Assad to make way for a democratic succession. He has rejected such calls as interference. Given Syria's location along fault lines of Middle East conflict, Western countries have shown no appetite for real intervention, such as with NATO air strikes that were key in the fall of Libya's Moammar Gadhafi to a popular revolt.