News outlets close to the Syrian regime and the Lebanese Shia militia Hizbollah, which has come to its support, said that "Operation Northern Storm" to retake Aleppo, the biggest city in the country, and the surrounding countryside had begun. Other sources told the AFP news agency that the battle would start in "the coming days or hours".
There was no evidence of a major attack last night, but there was renewed fighting near a government-held base on the north-western outskirts. Hizbollah reinforcements were said to have arrived in the area, while a video leaked to an opposition website showed a regime general recruiting men from two Shia towns to join in a fresh attack.
The regime is in high spirits after the Syrian army and Hizbollah retook Qusayr, close to the Lebanese border. They continued their advance over the weekend, sweeping through the last opposition-held villages north of the town.
They harried the retreating rebels and the thousands of civilians who had fled with them.
Syrian army soldiers drive a tank in the town of Qusayr (AFP)
Video posted online showed streams of people, mostly rebels and male civilians, marching dejectedly and in some cases staggering on crutches through the fields and orchards distinctive to the area, the sound of shelling in the background. In some, wounded men lay dying under trees.
Hadi Abdullah, one of the main opposition spokesmen in Qusayr, told The Daily Telegraph he was trapped in an enclave with 2,000 men, women and children. He said 110 people, including 40 women and children, had been killed when the refugee column was attacked by government forces on Saturday.
"We were a group of around 7,000 people," he said. "The first group of 1,000 got through (the encirclement) successfully. Then it was followed by another group but that came under direct fire from the regular army and Hizbollah forces.
"The dead and injured fell where they were. We could not even retrieve the bodies of women. The army tanks pulled some civilians and assassinated them. I called out for one of my relatives who was caught by the army. Someone from the other side answered saying, 'Come take him in pieces'."
State media at first claimed government forces had killed Abdulqader al-Saleh, also known as Hajji Marea, head of the biggest rebel brigade in Aleppo, and second-in-command of the military wing of the western-backed Syrian National Coalition.
Hajji Marea had led a group of reinforcements sent to help Qusayr's defence. The claim was later retracted, but rebels confirmed he had been injured.
The regime's recent fightback has cast doubt on the chances for a peace conference, backed by Britain, France and the United States, originally due to take place later this month in Geneva. Its date had already slipped back to next month, and William Hague, the Foreign Secretary, said regime advances reduced its chance of success.
"It makes it less likely that the regime will make enough concessions in such negotiations, and it makes it harder to get the opposition to come to the negotiations," he said.
He said he accepted demands by Tory MPs last week that a House of Commons vote be taken on any decision to arm the rebels.
"People have understandable concerns about the idea of sending arms to anybody in Syria and we'd all be very reluctant to do that," he said.
"On the other hand, at the moment, people are being killed in huge numbers while the world denies them the right to defend themselves."
The opposition says it cannot attend the conference under current circumstances.
"How can you imagine someone talks about a peace or political solution under this kind of war, this sectarian war?" George Sabra, the Coalition's acting head, said in Istanbul.
Separately a Lebanese man demonstrating against Hizbollah's participation in Syria was shot dead in Beirut, the first such incident in the Lebanese city.
