The Syrian military pounded rebel-held Sunni Muslim districts of Homs city for the 20th day today, despite international outrage over the previous day's death toll of more than 80, including two Western journalists, activists said.
Tanks pushed into part of the Baba Amro neighbourhood which has taken the brunt of the bombardment, activist Abu Imad said.
The plight of Homs and other embattled towns will dominate "Friends of Syria" talks in Tunis tomorrow involving the United States, European and Arab countries, Syria's neighbour Turkey and other nations clamouring for president Bashar al-Assad to halt the violence and relinquish power.
Russia, which along with China has vetoed two UN Security Council resolutions on Syria, has said it will not attend.
A United Nations report said today Syrian forces had shot dead unarmed women and children, shelled residential areas and tortured wounded protesters in hospital under orders issued at the "highest levels" of the army and government.
Rockets, artillery and mortar rounds rained on the Inshaat and Baba Amro districts, where Free Syrian Army rebels are entrenched. In the Khalidiya district mosques urged residents to take cover as mortar rounds started falling on the area.
"Explosions are shaking the whole of Homs. God have mercy," Abdallah al-Hadi said from the city.
Western diplomats said it had not yet been possible to evacuate three Western journalists wounded in Homs yesterday or extract the bodies of Marie Colvin, an American working for Britain's Sunday Times, and French photographer Remi Ochlik.
Those wounded in the rocket strike are British photographer Paul Conroy, reporter Edith Bouvier for French newspaper Le Figaro and Paris-based photographer William Daniels.
French president Nicolas Sarkozy said the journalists had been deliberately targeted in Baba Amro, a hotbed of opposition to Mr Assad, and demanded that the Syrian leader leave power."This regime must go," he said.
Footage shot by activists in Homs shows smashed buildings, empty streets and doctors treating casualties in makeshift clinics in Baba Amro after nearly three weeks of bombardment.
The Syrian Information Ministry said it "rejects accusations that Syria is responsible for the deaths of journalists who infiltrated into the country on their own responsibility, without the authorities knowing about their entry or location".
The state news agency said an officer and six other members of the security forces were killed tpdau by a bomb planted by "armed terrorists" near the northwestern city of Idlib.
In the United States, Republican presidential candidates Mitt Romney and Newt Gingrich advocated arming Syrian rebels.
"We need to work with Saudi Arabia and with Turkey to say, 'You guys provide the kind of weaponry that's needed to help the rebels inside Syria,'" Mr Romney said.
The White House, which so far has been against military intervention in Syria, has hinted that if a political solution were impossible it might have to consider other options.
In their report, independent UN investigators called for perpetrators of crimes against humanity in Syria to face prosecution and said they had drawn up a confidential list of names of commanding officers and officials alleged to be responsible.
"The commission received credible and consistent evidence identifying high- and mid-ranking members of the armed forces who ordered their subordinates to shoot at unarmed protesters, kill soldiers who refused to obey such orders, arrest persons without cause, mistreat detained persons and attack civilian neighbourhoods with indiscriminate tanks and machine-gun fire," it said in its 72-page report to the UN Human Rights Council.
Residents in Homs fear Mr Assad will subject the city to the same fate his late father Hafez inflicted on Hama, where many thousands were killed in the crushing of an armed Islamist revolt in 1982. The army is blocking medical supplies to parts of Homs and electricity is cut off 15 hours a day, activists say. Hospitals, schools, shops and government offices are closed.
The International Committee of the Red Cross has been trying to get the government and rebel forces to agree daily two-hour ceasefires. Access for aid workers will also be the focus of a planned visit to Syria by UN humanitarian chief Valerie Amos.
Mr Assad has called a referendum on a new constitution on Sunday, to be followed by a multi-party parliamentary election, which he says is a response to calls for reform. The plan is supported by his allies Russia and China but Western powers have dismissed it and the Syrian opposition has called for a boycott.
Reuters