Syrian government forces have launched an offensive in the city of Hama, as the shelling of opposition strongholds in the city of Homs continued, activists say.
Tanks deployed near the citadel of Hama were reportedly shelling the neighbourhoods of Faraya, Olailat, Bashoura and al-Hamidiya on Wednesday, and troops were advancing from the airport, opposition sources said.
Activists said no casualty reports were available from Hama, Syria's fourth largest city, because of communications problems.
Security forces also reportedly deployed in the Damascus neighbourhood of Barzeh in the morning, raiding homes and making arrests.
In Homs, which has emerged as the epicentre of the 11-month old uprising, the Revolutionary Council - the main opposition group co-ordinating the uprising there - said humanitarian conditions in the city were continuously getting worse, with a shortage of food and medical supplies.
The group said government forces pounded the neighbourhood of Bab Amr, a stronghold of the armed opposition, with mortars and gunfire for a 10th day on Wednesday in what it said was the worst assault so far on the area.
At least nine people were reportedly killed across the city.
Homs was also hit by an explosion at a major oil pipeline feeding a refinery near Bab Amr, residents said.
A large plume of smoke was rising from the fire at the pipeline, which runs near farmland at the edge of Bab Amr district, they said. It was not clear what caused the explosion.
A high presence of snipers was reported in the Inshaat neighbourhood, with residents displaced from the area saying their homes had been looted and sometimes occupied by government forces.
Referendum on constitution
Syria's state-run news agency said on Wednesday that President Bashar al-Assad has set February 26 as the date for a national referendum on the country's new draft constitution.
Parliamentary elections will be held within 90 days of the approval of the constitution, state television reported.
Al Jazeera's Rula Amin, reporting from Beirut in neighbouring Lebanon, said opposition figures inside Syria told her they did not want to take part in the referendum since they were not involved in drafting the draft.
"They say that if the president is serious about reform, they should have been allowed to take part in the process of drafting the constitution," our correspondent said.
"Still, this draft constitution is a major step if you look back in Syrian history. For the first time, it will allow for political pluralism, it will say the Syria from now on will be elected - not appointed by referendum - and there will have to be at least two candidates for the presidency.
"The government is trying to say that it's working on two parallel tracks - one is that it's proceeding with reforms, and the second track is that it's confronting armed groups - but that these tracks will not affect each other. That is the government line."
"The document was handed over to Assad last week by members of the drafting committee. The new draft reportedly leaves out a clause that says the ruling Baath Party is the 'leader of the nation and society'," Amin said.
Amendments to the constitution were a key demand by opposition groups at the beginning of the uprising against Assad in March, but the groups now say they accept nothing less than Assad's departure.
The UN General Assembly is due to debate and vote on a new resolution condemning the violence in Syria on Thursday.
The resolution is drafted by Qatar and Saudi Arabia, and "fully supports" the Arab League's plan promoted last month "to facilitate a Syrian-led political transition to a democratic, plural political system".
It "calls upon the Syrian government to immediately put an end to all human rights violations and attacks against civilians" and "condemns all violence, irrespective of where it comes from".
In-depth coverage of escalating violence across Syria
But the draft does not refer to an Arab League request for a joint peacekeeping mission with the UN, which has been met in some Western capitals with caution.
The General Assembly draft is similar to the one blocked by Russia and China in the UN Security Council on February 4. The two countries said the resolution against Damascus was "unbalanced".
While resolutions passed by the 193-nation General Assembly cannot be vetoed, they also carry less weight.
A resolution condemning the government crackdown on civilians in Syria was passed by the UN General Assembly in November, but violence has since continued unabated.
China's vice foreign minister cautioned on Tuesday that missteps by the Security Council could cause worse bloodshed in Syria.
Cui Tiankai reiterated China's position that Beijing supported the role of the Arab League in seeking to defuse the Syrian conflict and "inclusive dialogue" in Syria to end the violence. But he said the Security Council needed to take a "very careful and very responsible attitude".
"If the UN Security Council takes the wrong steps, that could lead to even worse bloodshed."
Earlier in the day, US President Barack Obama, meeting Xi Jinping, China's vice president in Washington, expressed disappointment about China's veto of the Security Council resolution on Syria.
State media reported that "large masses" gathered in the city of Latakia on Tuesday, rejecting foreign interference and denouncing the Arab role in the "conspiracy against Syria".
|A pro-government rally was held in the coastal
city of Latakia on Tuesday [AFP]
SANA news agency said participants carried Russian and Chinese flag, thanking these countries for their support.
Navi Pillay, the UN high commissioner for human rights, told the General Assembly on Monday that crimes against humanity had taken place since March 2011 and were continuing.
Bashar al-Jaafari, Syria's permanent representative to the UN, said Pillay's comments were unprincipled and insisted that Syria was coming under attack by terrorist organisations.
Addressing the General Assembly, Jaafari said: "After today, how can we trust the High Commissioner for Human Rights on issues related to defending and promoting human rights?"
He called on "all those who host, support, fund, indeed arm terrorist groups to cease forthwith in accordance with the resolutions of international legitimacy".
The Syrian government blames "armed terrorists" for the unrest in Syria that began after protests calling for reforms erupted across the country in March last year. Authorities say more than 2,000 security personnel have been killed, while opposition activists say more than 7,000 people, most of them civilians, have been killed.