Syrian forces and militiamen loyal to president Bashar al-Assad have been blamed for a "massacre" of at least 85 people, including women and children, in a Damascus suburb.

Both government and rebel sources confirmed that Syrian forces had mounted a major offensive against Jdaidet al-Fadl, and both sources said government troops had won the battle.

But opposition activists have described a "massacre" in the area and some say the death toll could be higher than 250.

"We documented 85 summarily executed, including 28 shot in a makeshift hospital after Assad's forces entered Jdeidet al-Fadel. We fear that the victims of the massacre are much higher," said Abu Ahmad al-Rabi, an activist in the adjacent district of Jdeidet Artouz.

Jamal al-Golani, a member of the Revolution Leadership Council opposition group, said the number of dead may be higher than 250, with many shot at close range, but the presence of army patrols made documenting all of them difficult.

Mr Golani said the killings happened over several days after pro-Assad forces stormed an area where there were up to 270 rebels.

He said he had counted 98 bodies in the streets and 86 people who he said had been summarily executed in makeshift clinics where they were lying wounded.

There was no immediate confirmation of the activists' account, although several videos uploaded to social media websites purported to show a number of bodies in body bags.

Spilling over

Meanwhile, the civil war has spilled into Lebanon as government troops advance on a town near the border.

The troops backed by fighters from the Lebanese Shiite militia, Hezbollah, are battling rebels for control of the town of Qusayr, just inside the Syrian border.

The area is a sectarian flashpoint and the main Syrian Opposition group says the cross border fighting could draw Lebanon into the civil war.

Many of the town's residents are Shiite Muslims.

Hezbollah says it has sent its fighters in to protect them from the rebels, who are mostly Sunnis.

The rebels are on the back-foot in the battle and have started firing rockets and artillery across the border into a Lebanese town, which is considered a Hezbollah stronghold.

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The cross-border fighting comes as Foreign Minister Bob Carr calls for an agreement on plans for the future of Syria.

Speaking at a meeting of European and Arab officials in Luxembourg, Senator Carr sought support for increased humanitarian aid, a post-Assad transition and commitments from the Syrian opposition to exclude Al Qaeda and refrain from using chemical weapons.

Senator Carr says the Syrian war has become one of the world's great humanitarian crises.

Under his plan, Australia would commit an additional $24 million to fund emergency medical and food supplies.

ABC/wires