Syrian troops pounded opposition areas, activists said, killing over 100 civilians in an offensive that has sent thousands of refugees surging into Turkey.

At least 15 rebels and 17 security force members were also killed, raising the death toll in violence to over 100.

Each side has accused the other of intensifying assaults in the run-up to a truce due to take effect early on Thursday, if government forces begin pulling back from towns 48 hours earlier in line with UN-Arab League envoy Kofi Annan's peace plan.

The military shelled Deir Baalba district in Homs, killing four people, the grassroots Local Coordination Committees opposition group said.

13 men were also found killed in the same area, it said.

Amateur activist video showed scenes of carnage said to be the aftermath of the shelling.

Mangled limbs and body parts in blankets were being loaded on a pick-up truck. A second video showed 13 men who appeared to have been tied up and executed.

No comment was immediately available from Syrian officials. The videos could not be independently verified. The government has placed tight restrictions on media access in Syria.

The Syrian Observatory for Human Rights said at least 74 civilians had been killed, including 40 in an army attack on al-Latmana, in Hama province, that began on Friday. The rebel Free Syrian Army lost 15 men in the battle, it said, and 17 members of the security forces were killed across the country.

In an activist video from al-Latmana, mourners held aloft the limp corpse of a child. A row of bodies lay on the ground.

The Observatory report said 12 were killed by shelling as the army swept through villages in Idlib province.

A rocket hit a bus travelling from Lebanon to Syria at Jousa just inside Syria, a Lebanese security source said. Witnesses said six Syrians were killed. Lebanese medics confirmed two dead and nine wounded. It was not clear who had fired the rocket.

Rebels trying to oust President Bashar al-Assad attacked army posts north of Aleppo before dawn, killing an officer and two men, and assaulted a helicopter base, activists said.

Syrian commandos shot dead three rebels in an overnight raid on a "terrorist den", Syria's state news SANA agency reported.

Country towns north of Aleppo have endured days of clashes and bombardment, prompting 3,000 civilians to flee over the Turkish border on Friday alone - about 10 times the daily number before Mr Assad accepted Mr Annan's plan 10 days ago.

The Syrian leader is fighting a popular uprising, which he blames on foreign-backed "terrorists", that has spawned an armed insurgency in response to violent repression of protests.

While many in Syria's Sunni Muslim majority back the revolt, especially in provincial areas, Assad retains support from his own minority Alawite sect and other minorities fearful that his overthrow would lead to civil war or Islamist rule.