Syrian President Bashar al-Assad's troops on Friday killed 15 pro-democracy protesters and army deserters, activists said, casting doubts on an Arab League plan accepted by Damascus to end the unrest in the country, dpa reported.
The head of the opposition Syrian National Council, Burhan Ghalioun, said Friday the Arab League "should give up hope" that the Syrian government will ever cooperate.
"It is clear that the Syrian regime is incapable of implementing any plan. It is in a real crisis," he told broadcaster Al Jazeera.
Western countries, led by the United States, have warned that the signs from Syria in the past two days were not encouraging, after reports of troops killing more than 33 civilians since Thursday.
"The Syrian troops have been shelling over the past 24 hours the province of Homs," Rami Abdel Rahman, a spokesman for the London-based Syrian Observatory for Human Rights, told dpa.
Eleven people were killed and more than 40 wounded when the Baba Amro neighbourhood in Homs was shelled, he added. Homs is a focal point of the protests against al-Assad's government.
Troops Friday fired on demonstrators in the city of Deir al-Zour, killing two people and arresting more than 50, according to Abdel Rahman.
In the Mediterranean coastal city of Banias, security forces surrounded a main mosque and beat worshippers as they attempted to demonstrate after the prayers, he said.
"The security forces also arrested dozens of people in Banias, including four children," the Syrian Observatory for Human Rights said.
Earlier Friday, two people were killed, one of them believed to be an army defector, when troops fired on people trying to cross the border into Jordan, according to the Syrian Observatory.
The continued government crackdown prompted some of the wounded in Homs to cross illegally to Lebanon for medical treatment, fearing that they might be arrested or tortured if they went to Syrian hospitals, opposition activists told dpa.
Video footage posted Friday on YouTube showed dozens of demonstrators, some of them masked, marching through the Midan district of the capital Damascus.
"How long is the Arab League going to listen to this liar (al-Assad)?" read a placard raised by one protester in the footage.
The Arab League plan, which was agreed to on Wednesday in Cairo, foresees a complete halt to the violence, the release of detained protesters, the withdrawal of army forces from civilian areas, and granting foreign media free access to Syria.
The state news agency SANA denied Friday's fatalities.
It quoted a statement by the Interior Ministry that an amnesty would be granted to anyone who handed in weapons to the authorities within one week.
The government has repeatedly blamed the unrest on "armed groups" allegedly financed by foreign powers.
More than 3,000 people, including at least 187 children, have been killed in the government crackdown on protesters since mid-March, according to the United Nations.