Syrian security forces stepped up a crackdown on Friday as activists said almost 110 people were killed in a two-day spike in violence ahead of a bid to condemn Damascus at the UN Security Council.

The head of the Arab League monitoring mission in Syria said that, since Tuesday, unrest had soared "in a significant way," especially in the flashpoint central cities of Homs and Hama and in the northern Idlib region.

The violence, which for the first time cost lives Friday in Aleppo, Syria's second-largest city, "does not help ... to get all sides to sit at the negotiating table," General Mohammed Ahmed Mustafa al-Dabi said.

For the second day, Syrian forces kept up their attacks on Homs, where dozens have died, as Western and Arab states rushed to unveil a draft UN resolution to condemn a crackdown that has killed more than 5,400 since March.

The pre-dawn assault on Homs, and reports of similar offensives against Hama and other cities, came hours after the United Nations said it could no longer keep track of the death toll.

The Syrian Observatory of Human Rights said in its latest count that security forces killed at least 34 civilians on Friday, while 12 soldiers were killed in attacks on the military.

It said 19 people died in the southern province of Daraa, five in Aleppo, north Syria, five in Homs, three in Douma, just north of Damascus, including a child and woman, a boy on the outskirts of the capital, and another in Hama.

The majority of civilian casualties were protesters shot by security forces.

Six soldiers died in a car bomb attack on a security checkpoint in the city of Idlib and another six were killed in Daraa province in clashes with army deserters, the Britain-based watchdog's Rami Abdel Rahman told AFP.

In violence across the country on Thursday, the Observatory said 62 people were killed, including 33 in Homs.

The Observatory said Hama, also came under assault by security forces early on Friday, with intense firing from heavy machineguns and loud explosions heard.

On the outskirts of Damascus, an 11-year-old boy was killed at a checkpoint in Hamuriyeh, it said in statements received in Nicosia.

At least 384 children have been among the dead in the uprising against President Bashar al-Assad's regime, and almost the same number detained, the United Nations Children's Fund (UNICEF) said on Friday.

"As of January 7, 384 children have been killed; most are boys," Rima Salah, acting UNICEF deputy executive director, said in Geneva. She said about 380 children have been detained, "some less than 14 years old."

The Syrian National Council, the biggest opposition umbrella group, condemned the offensives against opposition strongholds and said it was in contact with members of the Security Council to press for strong condemnation.

The latest wave in the government crackdown, now in its 11th month, comes as the West tries to ride diplomatic momentum sparked by last weekend's surprise call by the Arab League for Assad to step down.

Western and Arab nations were to hold talks in New York later Friday on a draft resolution denouncing the Assad regime that has been blocked by strong resistance from Damascus allies Beijing and Moscow.

In Cairo, where the Arab League is based, scores of Syrian regime opponents stormed their country's embassy, an AFP reporter said.

At least 200 Syrian protesters forced their way into the building in Garden City neighbourhood, breaking doors and windows, before security officials arrived at the mission and expelled them.

The mission was empty for the Muslim weekend.

Syrian ambassador Yusef Ahmed visited the mission after the incident and said he would formally complain to Egyptian authorities. "The protection today was very weak," he told AFP.

The Security Council's five permanent members -- Britain, China, France, Russia and the United States -- met Thursday.

UN chief Ban Ki-moon urged the Security Council, where diplomats hope for a vote early next week, to speak with one voice on Syria. "We have to seize this moment," he said.

But a senior Russian diplomat warned that the draft still falls short because it refers to sanctions and warns of further measures, raising the spectre of military action.

That has been a red line for Moscow ever since a UN resolution help justify a military intervention in Libya last year.

If the draft is agreed, the council would say it "fully supports" the Arab League plan of January 22 that calls on Assad to hand over his powers to his deputy so that a national unity government can be formed and elections held.

But Russian Deputy Foreign Minister Gennady Gatilov Gatilov said "we cannot support any UN resolution calling for the support of Assad's resignation," adding that a quick vote on the Western-Arab draft was "destined for failure."