A government mortar attack in the Syrian town of Rastan has killed 12 people, including five children, AFP has reported.
Extremely graphic and disturbing video of the attack was posted online.
While it was not possible for the Huffington Post UK to verify the video, it showed a gathering of hundreds of protesters in what appeared to be a large warehouse.
The protesters are pictured singing and waving peace signs when a sudden explosion from what appeared to be a mortar shell shattered the building and exploded.
Many of the protesters immediately fled the scene, but some ran to the crater and appeared to be dragging away bodies of those injured or killed.
The footage showed a bloody and brutal aftermath. Other videos posted later included even more gruesome details of human remains and body parts.
Very large protests were also reported elsewhere in Syria, including in Hama where hundreds gathered to call for the arming of the Free Syrian Army:
Other large-scale protests were reported in Aleppo and in the capital Damascus.
Around 4,000 residents in Baba Amr were left behind after the Free Syrian Army was forced to flee, and now live in fear of a "massacre", said the Syrian National Council.
The Red Cross said that a convoy of seven trucks carrying aid to Homs had reached the city on Friday and were attempting to distribute help to the civilians.
But the president of the Red Cross later told Sky news that its vehicles were not able to enter the critical Baba Amr neighbourhood to help the people there, after being stopped by government forces.
The UN said it was alarmed at reports of summary executions taking place in Homs and was trying to investigate.
Earlier France said it will close its embassy in Damascus after three weeks of bloody shelling by government forces saw rebel fighters forced to withdraw from the city of Homs.
President Nicolas Sarkozy made the announcement at an EU summit where new sanctions against the regime are being discussed and where Prime Minister David Cameron said Syrian president Bashar al-Assad should expect "a day of reckoning".
The French foreign ministry also announced that the two French journalists evacuated from Homs on Thursday will return to France on Friday.
Meanwhile the bodies of two journalists killed in Homs, Sunday Times reporter Marie Colvin and French photographer Remi Ochlik, have been handed over to the International Committee of the Red Cross by the Syrian authorities and are being taken to Damascus, a spokesman for the charity said.
The news follows the widespread broadcast of two videos supposedly depicting Syrians burying both of the bodies on Thursday.
The United Nations estimates at least 7,500 people have been killed since the start of the uprising in March 2011. Activists put the total dead closer to 9,000, with thousands more still detained or missing.
The protests reported around the country include:
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