Syria on Friday amassed troops in the northern city of Aleppo in preparation for an onslaught on rebel-held areas and the opposition reported a massacre in the central city of Hama.
Opposition activists said more than 62 people, including women and children, were killed in a massacre committed by forces loyal to President Bashar Assad in Hama. The claim by the Local Coordination Committees could not be independently verified.
In Aleppo, Syria's main commercial center, the Syrian army sent more troops and tanks to break a stalemate in fighting with rebels holding out for six days in opposition areas mainly in the east and southwest of the city near the border with Turkey.
"Dozens of trucks loaded with troops and backed by more than 100 tanks are being positioned around Aleppo," Abu Omar al-Halabi, a commander in the rebel Free Syrian Army, told dpa by phone.
The United Nations General Assembly will Friday vote on a resolution condemning Assad. The non-binding vote comes one day after UN-Arab League envoy for Syria Kofi Annan resigned after more than five months of diplomacy failed to stop the bloodshed.
Annan drafted a six-point peace plan that included a ceasefire announced in April but never took hold. His plan became increasingly irrelevant over the last few weeks as fighting escalated in the capital Damascus and Aleppo.
Deadlock between Western powers and Syria's allies Russia and China at the UN Security Council has prevented passage of a resolution on the crisis. Russia and China vetoed three Western- and Arab-backed resolutions condemning Assad and threatening sanctions.
The vote at the General Assembly is seen as an attempt to put more pressure on the UN Security Council to take action.
The government offensive in Aleppo comes after it recaptured several rebel-held areas in Damascus in a large-scale military operation.
"The focus two weeks ago was on Damascus. The focus is now on Aleppo, where there has been a considerable build-up of military means, and where we have reason to believe that the main battle is about to start," UN peacekeeping chief Herve Ladsous said on Thursday.
The opposition Syrian Observatory for Human Rights reported clashes in the eastern district of Jdeidet Artouz in the capital.
Activists said 20 people were killed in government shelling attack on a Palestinian refugee camp in the south of Damascus.
Assad's forces have been carrying out house-to-house raids in Damascus since last month when a bomb attack killed four top security officials from Assad's inner circle.
Russia, which blames the violence on Western backing for the rebels, said Annan's resignation could increase the chance of a military intervention in Syria.
"He is an honest international intermediary, but there are those who want to remove him from the game so as to free their hands to use force. This is already clear," Deputy Foreign Minister Gennady Gatilov wrote on Twitter.
China expressed regret over Annan's resignation and renewed its call for a political solution to the 17-month conflict.
The UN General Assembly is also likely to call on the Syrian government not to use chemical and biological weapons.
The draft, backed by Arab powers, also calls on Syria to initiate talks with the opposition that lead to a transition to democracy.
Annan Friday said that the "stalemate" can still be overcome if all sides are prepared for "genuine compromise."
Writing in the Financial Times, he urged Russia, China and Iran to make "concerted efforts to persuade Syria's leadership to change course and embrace a political transition."
Foreign Secretary William Hague said Britain would step up its "non-lethal" support for Syrian rebels.
The pledge comes two days after media reports said U.S. President Barack Obama had signed an order, allowing the CIA and other agencies to provide clandestine support to the Syria revolt.
Want to enjoy 'Zen' reading - with no ads and just the article? Subscribe todaySubscribe now