At least 28 people have been killed by Syrian government shelling and offensives against rebel-held towns, activists said today.
The news came as the US posted online satellite images of troop deployments that cast further doubt on whether the regime intends to comply with an internationally sponsored peace plan.
Syrian president Bashar Assad has accepted a ceasefire deadline brokered by international envoy Kofi Annan, which calls for his forces to pull out of towns and cities by Tuesday and for both government and rebels to lay down their arms by 6am local time on Thursday.
But the escalating violence of the past few days has fuelled accusations that Assad is rushing to stamp out as much of the year-old uprising against him as he can before next week's ceasefire.
The Syrian government said it has begun to withdraw forces ahead of the ceasefire but activists say no significant pullouts have taken place and troops, checkpoints and snipers remain in almost all major flashpoint towns and cities.
"They are systematically trying to crush the revolt wherever they can and regardless of the human cost," said activist Mohammad Saeed in the Damascus suburb of Douma.
US ambassador to Syria Robert Ford said the Syrian government appears to have pulled back some of its forces from towns and cities but in other places has kept them in place or simply shifted around troops and armoured vehicles.
He said he was basing his information on satellite images before and after the alleged pullouts which were posted on the US Embassy Facebook page.
Arrests, sweeps and the artillery bombardment of opposition strongholds have continued, Mr Ford's statement said.
"This is not the reduction in offensive Syrian government security operations that all agree must be the first step for the Annan initiative to succeed," the statement said.
"The regime and the Syrian people should know that we are watching. The regime cannot hide the truth," it added.
Western leaders along with the Syrian opposition have cast doubt on Assad's intentions, suggesting he is playing for time and is not serious about the plan, which aims to pave the way for talks between the regime and the opposition on a political solution.
The government has launched offensives in several parts of the country in the past few days in a desperate attempt to crush the rebels.
The Local Coordination Committees said shelling today by government forces killed at least 24 people in the village of al-Latamneh in the suburbs of the restive city of Hama. The British-based Syrian Observatory for Human Rights put the number of deaths at 27. It said most were killed by shells fired as troops tried to storm al-Latamneh following clashes with defectors there over the past two days.
In the nearby province of Homs, activists also reported shelling of the rebel-held areas of Rastan, Deir Baalabeh and Qusair, where they said four people including a mother and her son were killed.
Violence was also reported in the northern province of Idlib. The offensive there has triggered a massive wave of refugees who crossed the border to Turkey in the past few days with horrific accounts of mass graves, massacres and burned-out homes.
Activists have reported about 100 dead in the villages of Taftanaz and Killi, both in Idlib, in recent days.
The escalating violence has dimmed hopes that the fighting, which the UN says has killed more than 9,000 people, will end anytime soon. The country appears to be spiralling towards civil war - a fearsome development that could bring a regional conflagration.
Ambassador Ford urged Assad to allow a UN monitoring force into the country and to give it full access to investigate the regime's compliance with the peace plan.
Yesterday, a small UN advance team headed by a Norwegian major general, Robert Mood, met with Syria's deputy foreign minister to discuss the ceasefire plans. Maj Gen Mood is to set up a UN monitoring force with 200 to 250 members if the peace plan succeeds.