A plan to end the violence in Syria was in ruins on Monday after rebels rejected last-minute demands by President Bashar al-Assad ahead of a critical deadline.
In a sign of the deteriorating chances for peace, Syrian forces reportedly opened fire on refugees who had crossed the border into a Turkish camp.
Two Syrian refugees and one Turkish translator were injured, according to Turkish officials, in the camp near the town of Kilis in the southwest of the country.
The ceasefire plan, brokered by UN and Arab League special envoy Kofi Annan, had been endorsed by the Security Council, including Russian and China, and agreed in principle by the government and the rebels.
It was intended the plan would begin with a withdrawal of government troops from civilian areas on Tuesday and be followed by a ceasefire 48 hours later.
But the Syrian Foreign Ministry changed its demands on Sunday and said it would need written guarantees from the rebels that they would put down their weapons.
"To say that Syria will pull back its forces from towns on 10 April is inaccurate," the ministry said in a statement. "Kofi Annan having not yet presented guarantees on the acceptance by armed groups to a halt of all violence."
That call for fresh guarantees was swiftly rejected by several rebel groups, including the Free Syrian Army , whose commander Riad al-Assad said from Turkey that it did not recognise the regime or trust it would honour any ceasefire.
"We are committed to the Annan plan," Col Riad al-Asaad said. "We will present our guarantees and our commitments to the international community, but not to this regime."
On Monday China called for Syria to honour the agreement, but hopes were low that the violence would draw to a close on deadline.
Opposition groups and activists reported sustained violence across the country on Sunday and Monday morning, including in the suburbs of the capital Damascus.
"Mortar rounds are falling like rain," activist Tarek Badrakhan told the AP news agency from Homs. Assad's forces are planning "to kill and commit massacres," he said.
From Homs activists leaked video to YouTube on 8 April appearing to show government troops mocking rebels as they held a man to the ground, set him alight and cut his throat as he burned.
In another video regime troops appeared to strap a dead rebel to the front of a tank while shouting support for the Assad government.
The horrific clips were linked to by the Activist News Association, but it was not possible to independently verify their accuracy.
Shopkeepers in Damascus also uploaded video purporting to show their businesses having been broken into and looted by government troops.
Opposition members reported the the regime deployed helicopters and tanks in the north of the country as it assaulted rebel positions in the town of Kafarnaya.
The use of mortars and rockets was also reported, while in Damascus activists said troops opened fire with machine-guns while conducting arrests of suspected rebels.
An activist group known as the Syrian Network for Human Rights reported 50 casualties across Syria on Sunday, including 15 dead in Homs and 22 dead in Iblib.
Five people were also reported dead in the Bait Jinn suburb of Damascus, six in Hama and one each in Aleppo and Dar'aa, the group said.
The London-based Strategic Research & Communication Centre said that 24,000 Syrian citizens had fled to Turkey as violence escalated in the north of the country.
According to the UN more than 9,000 people have been killed in Syria since the uprising against Assad's government began in March 2011.