By Oliver Holmes
BEIRUT (Reuters) - Syrian forces swept through the corpse-strewn streets of nearly-deserted opposition districts on the outskirts of the capital on Sunday, as the conflict enters a new phase of heavier fighting near Bashar al-Assad's seat of power.
Government troops also bombed and shelled other towns across the country, a day after Russian diplomats rode again to Assad's rescue, blocking language at a meeting of world powers that would have called on the president to leave power.
Sixteen months into an uprising against Assad in which more than 10,000 people have been killed, intensive fighting and shelling has now reached the outskirts of Damascus. New tension has also built up on the frontier with Turkey in recent days after Syrian forces shot down a Turkish jet.
Residents of the Zamalka district on the capital's outskirts were struggling on Sunday to bury dozens of people killed the day before in a mortar attack on an anti-Assad march, opposition activist Susan Ahmad said by phone from the Damascus suburbs.
More than 40 people were killed in the attack on Saturday when security forces fired a mortar bomb into a funeral procession in Zamalka for a man who had been killed in shelling, activists said.
"It is really bad today across Damascus," said Ahmad. "Zamalka was like a massacre, but we couldn't bury all of the martyrs as it is dangerous to be out on the streets and we can't treat the wounded. There is no medicine."
Government troops were raiding Zamalka and Douma, a town of half a million people on the outskirts of Damascus that now stands almost empty after siege and shelling as the army tried to root out rebels, she said.
"Douma is completely destroyed," said Ahmad. "If you go to Douma you can smell the bodies. It's really like a ghost city."
On Saturday, Free Syrian Army fighters fled the town and residents said they feared a massacre at the hands of troops entering it.
Turkey said on Sunday it had scrambled F-16 fighters near the frontier the previous day in response to three separate incidents after Syrian helicopters approached the border.
Turkey, a NATO member that has turned against Assad and allowed its territory to become a rear base for rebels, has mobilized since Syrian forces shot down one of its jets 10 days ago. It sent forces towards the border this week and said it would treat Syrian troops approaching the frontier as hostile.
Top level diplomacy has so far been futile, and a much-anticipated meeting in Geneva on Saturday showed that Western and Arab states had yet to persuade Russia and China to drop support for Assad.
The two countries have repeatedly used veto power at the U.N. Security Council to block calls for Assad to leave power.
The meeting, convened by peace envoy Kofi Annan, agreed that Syria should seek a transitional unity government, but Moscow and Beijing successfully blocked language that would have suggested the new arrangement should exclude Assad.
Western officials say the text agreed at the talks - billed as a last-ditch effort to halt the worsening violence - still implies indirectly that Assad should stand down, but Moscow says it does no such thing.
The Syrian Observatory for Human Rights, an anti-Assad violence monitoring group in Britain, said more than 150 people had been killed on Saturday and Sunday. It said there was shelling in southern Deraa province and the central city of Homs, long the focus of previous crackdowns.
"We can hear bombing in different areas of Homs city today," said Waleed Fares, an opposition activists who lives in the central Khalidiya district of Homs. The Syrian authorities severely restrict the media, making it extremely difficult to verify such reports.
"There are three-storey building that have fallen down as the Syrian army is using large mortars," he said, adding that seven people had been killed on Sunday and 14 more wounded.
Efforts by International Committee of the Red Cross (ICRC) to evacuate civilians and wounded from Homs have failed twice since the humanitarian group said it had obtained assurances on June 20 from both authorities and rebel forces that their convoys would be allowed access.
Violence prevented safe passage on both attempts, the Red Cross said.
Activist Fares says civilians are trapped in the heart of the city as the army has surrounded central districts and positioned snipers on roofs to shoot people in the street.
"There is no safe place for civilians to go," he said via Skype.
Russian Foreign Minister Sergei Lavrov said on Saturday the Geneva agreement did not imply at all that Assad should step down, as there were no preconditions excluding any group from the proposed national unity government.
Nevertheless, French Foreign Minister Laurent Fabius said the creation of a unity government would imply an end to Assad's rule, because the opposition would not join unless he goes.
"The opposition will never agree to him, so it signals implicitly that Assad must go and that he is finished," Fabius told television station TF1 on Sunday.
Peace envoy Annan, a former U.N. secretary-general, said after the Geneva talks the transitional government should include members of Assad's administration and the Syrian opposition and that it should arrange free elections.
"Time is running out. The conflict must be resolved through peaceful dialogue and negotiations," Annan told reporters.
Annan's plan is the only international peace effort on the table, but has been essentially ignored by Assad's government, with a ceasefire that failed to hold and a small team of unarmed U.N. monitors announcing they could not do their job.
(Additional reporting by Khaled Yacoub Oweis in Reyhanli, Turkey, John Irish in Paris and Stephanie Nebehay and Tom Miles in Geneva; Writing by Oliver Holmes; Editing by Peter Graff)