AMMAN (Reuters) - Syrian security forces killed at least 16 civilians in attacks on tens of thousands of protesters demonstrating against the rule of President Bashar al-Assad on the first Friday of the Muslim fasting month of Ramadan, activists said.
A six-day tank assault on the central city of Hama to crush pro-democracy demonstrations there has killed at least 300 civilians, the Local Coordination Committees, an activists' group, said, citing refugees from the conflict.
The Syrian Revolution Coordinating Union said government forces shot dead two protesters and wounded 12 after evening Ramadan prayers in the Maydan district of central Damascus, which has become a focal point of demonstrations despite the deployment of ultra-loyalist Republican Guards in the area.
Security forces also fired at people protesting after evening prayers in the capital's suburbs of Harasta, Douma and Daria, residents said.
Tanks shelled the city of Hama for a sixth day. Hama residents feared higher casualty figures than the 135 estimated killed since the military assault began Sunday on the city of 700,000 people in central Syria.
The Syrian protesters are defying a bloody military crackdown on uprisings that began in March against some 41 years of Assad family domination.
U.S. President Barack Obama, French President Nicolas Sarkozy and German Chancellor Angela Merkel agreed to consider further steps to pressure Assad over his crackdown, the White House said, without elaborating on the measures to be taken.
The United States extended sanctions against Syria on Thursday to include a prominent businessman in the fourth round of sanctions which have targeted Assad, his brother Mahir, top government officials and security forces.
Obama held separate phone calls with the European leaders and they all condemned the Syrian government's "indiscriminate violence against the Syrian people," it said.
Turkish Foreign Minister Ahmet Davutoglu, whose government once strongly supported Assad, said: "The developments there are unacceptable... Syria needs to take the messages from Turkey and international community seriously."
The Local Coordination Committees said seven protesters were killed in an eastern suburb of Damascus and three in the town of Dumair north of the capital.
In Homs, 165 km (100 miles) north of Damascus, where tanks and armored vehicles deployed two months ago to crush dissent against Assad, two protesters were killed. A protester was also shot dead in the southern Hauran plain, cradle of the five-month uprising for political freedoms, the organization said.
They said demonstrations were staged also in the eastern tribal province of Deir al-Zor where tanks assembled at the gates of the provincial capital, in the southern Hauran plain, in Homs and its rural environs, in the coastal cities of Jableh and Latakis and in several districts of the capital Damascus.
"We are not scared, God is with us!" protesters shouted. They also chanted in support of Hama and called on Assad to go. "You Syrian raise your hand, we do not want Bashar!" they chanted in live footage broadcast on Al Jazeera television.
Hama, traditionally a center of majority Sunni Muslim opposition to the domination of Assad's minority Alawite sect, is where his father, the late Hafez al-Assad, sent in tanks and killed thousands to crush a rebellion in 1982.
"They are hitting (Hama's) al-Hader district and neighborhoods around the Aleppo road. Electricity is still cut off," one resident told Reuters in a call via satellite phone.
A witness told Al Jazeera that the army had banned protests in Hama and was not allowing people to gather in mosques in case
they would start marching from there after prayers.
The continued military assaults against civilian unrest ignored rising international condemnation over the attacks that Washington said had killed 2,000 people during the revolt.
Syrian authorities have expelled most independent media since the unrest erupted, making it difficult to verify witness accounts and official statements.
In Geneva, U.N. human rights investigators said Syrian forces must stop using excessive force against peaceful protesters that has resulted in executions and other crimes punishable under international law.
In a joint statement, the independent experts called on the Syrian authorities to halt their violent crackdown, including the "indiscriminate use of heavy artillery."
Syrian authorities say the army swept into Hama to confront "armed terrorist groups" attacking civilians and sabotaging property. They say 20 soldiers have been killed.
The official news agency said two security police were killed in an ambush by an "armed terrorist group" on the main northern highway near the town of Maarat al-Numan, 70 km (40 miles) north of Hama.
Their patrol had gone to the highway "in response to calls by citizens after several cars were subjected to theft and terror on the highway," the agency said.
Syrian authorities blame armed groups and Islamists for the violence and say 500 soldiers and police have been killed.
Additional reporting by Suleiman al-Khalidi, Dominic Evans and Mariam Karouny in Beirut, Stephanie Nebehay in Geneva; Editing by Gareth Jones