Hundreds of people have been killed or injured in a major army offensive in the central Syrian city of Homs, activists say.
Activists talking to Al Jazeera on Saturday said the army had used tanks, mortars and machine guns in the assault on the Khaldiyeh neighbourhood, which began on Friday night and continued overnight.
Al Jazeera's Mysa Khalaf, reporting from Beirut in neighbouring Lebanon, said sources in Syria told her bombardment of the area started after the opposition Free Syrian Army attacked Syrian army checkpoints and killed about 10 soldiers.
"Since then, it seems that Khaldiyeh has been under constant bombardment," she said."Several buildings have been destroyed.
"I've been told that the main public hospital is completely overwhelmed and people have set up makeshift clinics in mosques. They are running low on supplies of blood."
As reports of the violence spread, the Tunisian foreign minister has announced that his government started the procedure for expelling the Syrian ambassador from Tunis.
Rafeeq Abdel Salaam told Al Jazeera that the decision will be "implemented in near future by ministry of foreign affairs".
Meanwhile, angry protesters stormed the Syrian embassy in Cairo, the Egyptian capital, and staged demonstrations outside the embassies in the UK and the US, demanding an end to the deaths.
Stones were thrown at the building during the demonstration in London.
Hadi al-Abdallah, an activist in Homs, told Al Jazeera that army defectors had captured 19 members of the security forces earlier in the day.
Activists said government forces were targeting the neighbourhoods of Bab Tadmour, Bab Dreib, and Karm el-Shami simultaneously, as the military campaign in Khaldiyeh intensified.
Video purportedly showing a building on fire in al-Inshaat neighbourhood was posted online, after activists said the area was also shelled by government forces.
"There has been non-stop bombardment in Bab Amr [neighbourhood of Homs] ... They've been bombarding Bab Amr and Khaldiyeh non-stop with mortar bombs and tank shells ... it's just random bombarding on rooftops," Danny Abdul Dayem, an activist, told Al Jazeera early on Saturday.
The UK-based Syrian Observatory for Human Rights said 14 soldiers were killed in clashes with opposition fighters and that five army defectors had lost their lives.
The group cited witnesses saying 217 people had been killed in Homs, 138 of them in Khaldiyeh.
The opposition Syrian National Council decried Saturday's violence as a "horrific massacre".
"The Syrian National Council calls on everyone around the world to speak up and do something to stop the bloodshed of innocent Syrians," it said in a statement.
Homs is one of the flashpoint cities in Syria's uprising, and some areas, including Khaldiyeh, have become strongholds of the armed opposition.
The official SANA news agency blamed "armed terrorist groups" for the violence, and reported that media reports were "distortion [and] falsification".
The government "denies shelling by the army in certain districts of Homs, as peddled by television stations that are inciting" violence", the channel reported.
"The civilians shown by satellite television stations are citizens who were kidnapped and killed by armed gunmen."
The Syrian government said that most of those killed in Homs had been civilians and soldiers who were being held prisoner by the so-called "Free Syrian Army", the armed opposition.
In a bid to halt the escalating violence, diplomats at the UN Security Council in New York have for days been debating a draft resolution condemning human rights violations in Syria.
Al Jazeera meets activists in Homs who are defying bullets to document violence
A vote on the latest draft was expected as the council was due to meet in New York on Saturday.
On Friday, a senior US state department official said his country was "cautiously optimistic" that Syria's ally, Russia, would support the resolution.
The latest draft does not explicitly call on Assad to step down or mention an arms embargo or sanctions, though it "fully supports" an Arab League plan to facilitate a democratic transition.
Speaking on conditions of anonymity, the official said: "From our perspective, this meets the objective of supporting the demands of the Syrian people and the Arab League ... providing a peaceful Syrian-led political path forward."
Sergei Lavrov, the Russian foreign minister, said on Saturday, however, that the text of the resolution still did not "suit" Moscow, and warned of a "scandal" if it was put to a vote.
In its statement, the SNC demanded that Russia "clearly condemn the regime and hold it responsible for the massacres".
Activists in Homs have been calling for foreign intervention to stop the violence there.
"We want any kind of intervention by any kind of troops. We want anyone to help us. Our Free Syrian Army only has Kalashnikovs, has machine guns. Some RPGs, some rockets" Dayem told Al Jazeera.
"They cannot fight the whole Syrian army, that has tanks, that has planes. We want anyone to come in and help us.
"Civilians are dying, women are dying, kids are dying. Why isn't anyone doing anything about this? No-one is helping us."
On Friday, thousands of protesters took to the streets across Syria to commemorate the 1982 massacre in the city of Hama, ordered by late President Hafez al-Assad, that killed tens of thousands.
"While we commemorate Hama massacres, the son [President Bashar al-Assad] is imitating his father," Burhan Ghallioun, the head of the Syrian National Council, the main opposition bloc, told Al Jazeera.
The whole city [Homs] is being targeted by heavy weaponry. The hospitals are in siege by the regime tanks. They want the injured to become dead."