BEIRUT — Syrian forces pushed dissident troops back from the edge of Damascus in heavy fighting Monday, escalating efforts to take back control of the capital’s eastern doorstep ahead of key U.N. talks over a draft resolution demanding that President Bashar Assad step aside.

Gunfire and the boom of shelling rang out in several suburbs on Damascus’ outskirts that have come under the domination of anti-regime fighters. Gunmen — apparently army defectors — were shown firing back in amateur videos posted online by activists. In one video, a government tank on the snow-dusted mountain plateau towering over the capital fired at one of the suburbs below.

As the bloodshed increased, with activists reporting more than 40 civilians killed Monday, Western and Arab countries stepped up pressure on Assad’s ally Russia to overcome its opposition to the resolution.

U.S. Secretary of State Hillary Rodham Clinton and the British and French foreign ministers were heading to New York to push for backing of the measure during talks Tuesday at the United Nations.

“The status quo is unsustainable,” Clinton said, saying the Assad regime was preventing a peaceful transition and warning that the resulting instability could “spill over throughout the region.”

The draft resolution demands that Assad halt the crackdown and implement an Arab peace plan that calls for him to hand over power to his vice president and allow creation of a unity government to pave the way for elections.

If Assad fails to comply within 15 days, the council would consider “further measures,” a reference to a possible move to impose economic or other sanctions.

Pro-Assad forces have fought for three days to take back a string of suburbs on the eastern approach to Damascus, mostly poorer, Sunni-majority communities. In past weeks, army defectors — masked men in military attire wielding assault rifles — set up checkpoints in the communities, defending protesters and virtually seizing control.

Late Sunday, government troops retook two of the districts closest to Damascus, Ein Tarma and Kfar Batna, said Rami Abdul-Rahman, the London-based head of the Syrian Human Rights Observatory, which tracks violence through contacts on the ground.

On Monday, the regime forces were trying to retake the next suburbs out, pounding neighborhoods with shelling and heavy machine guns in the districts of Saqba, Arbeen and Hamouriya, he said.

At least five civilians were killed in the fighting near Damascus, according to the Observatory and another activist group, the Local Coordination Committees.

Regime forces also heavily shelled buildings and battled dissidents in the central city of Homs, one of the main hot spots of the uprising, activists said.

The reports could not be independently confirmed. Syrian authorities keep tight control on the media and have banned many foreign journalists from entering the country.