The head of the Arab League has warned that Syria may be sliding towards civil war, as security forces fired on thousands of people who poured into the streets in support of army defectors.
Over the course of the 10-month-old uprising, much of the violence has been from security forces firing on unarmed protesters.
But in recent months breakaway soldiers have been attacking the Syrian military, and some opposition members have taken up arms against the regime, adding to the violence.
Despite that, President Bashar Assad appears to maintain a firm grip on power in the face of growing international pressure to halt his crackdown and step down.
The Arab League chief, Nabil Elaraby, said that Assad's regime was either not complying or only partially complying with an Arab League plan that Syria signed last month to end its crackdown.
"We are very concerned because there were certain commitments that were not complied with," he said in Cairo, where the League is based. "If this continues, it may turn into civil war."
The UN estimates more than 5,000 people have been killed since the uprising began in March.
The British-based Syrian Observatory for Human Rights said security forces killed one protester in the town of Ariha in the north-western province of Idlib, where more than 20,000 people were demonstrating on Friday.
The Observatory reported violence in the southern province of Daraa, the eastern region of Deir el-Zour and the central province of Homs, all centres of frequent protests.
The Arab League plan calls for removing Syrian forces and heavy weapons from city streets, starting talks with opposition leaders and allowing human rights workers and journalists into the country.