By Erika Solomon and Mariam Karouny
BEIRUT, July 16 (Reuters) - Clashes between rebels and government forces erupted for a second day in the Syrian capital on Monday, activists said, in some of the fiercest fighting to hit Damascus since the 17-month-old revolt against President Bashar al-Assad began.
Armoured vehicles rolled into the southern district of Midan and snipers deployed on rooftops, residents said. Heavy machine gun fire could be heard in video uploaded by activists in the area.
"Security forces entered the neighbourhood, there is a real war going on right now," a resident in Midan said.
The spread of fighting in the capital came as United Nations peace envoy Kofi Annan starts a two-day visit to Moscow. He will meet Russian President Vladimir Putin, who has resisted Western calls to increase pressure on Assad.
Russian Foreign Minister Sergei Lavrov signalled no change in its position on the conflict before talks with Annan.
Lavrov said Western efforts to pass a Security Council resolution to extend the U.N. monitoring mission in Syria, which includes a threat of sanctions, contained "elements of blackmail". He called for support of Moscow's resolution instead, which does not call for sanctions.
"If our partners decide to block our resolution no matter what, then the U.N. mission will not have a mandate and will have to leave Syria. That would be a pity," he said.
The monitoring mission was suspended due to rising violence in Syria, where activists say more than 17,000 people have died.
At least five people were killed and dozens more wounded in Sunday's fighting. Activists said they expected more casualties from the fighting on Monday, but could not give an estimate yet.
One activist, who also asked not to be identified, said residents were preparing for more trouble in the capital after the army crushed pockets of revolt in suburbs outside Damascus, such as Douma.
"There were thousands of fighters in some of those suburbs. Some of them were killed but a lot of them fled and they've been heading to the capital itself," the activist said.
Activists said angry protesters blocked the international highway to Jordan in solidarity with the residents of Midan and Zahera neighbourhoods, where there were continued clashes.
"Smoke is rising from the area. People are blocking this road with rocks and burning tyres hoping to lighten the pressure on Midan," said activist Samir al-Shami, speaking by Skype.
Accounts in Syria are difficult to verify because the government has restricted access to international media.
Pressure on Assad has been growing both from outside the government and within.
Morocco asked Syria's ambassador to the country to leave and declared him persona non grata. The move comes days after the Syrian ambassador to Iraq defected to the opposition, and a week after top general and Assad insider Manaf Tlas fled Syria.
Rising violence in Syria, including several alleged massacres in the country, has increased outrage in Syria. What began as peaceful protests has morphed into an armed insurgency fighting back fiercely against Assad's heavy crackdown.
The International Committee for the Red Cross now classifies the conflict in Syria as a civil war.
Annan is visiting Moscow just days after opposition reported a new massacre in the village of Tremseh which prompted a fresh wave of denunciations in the West, where diplomats still hope Russia might ease support for Assad.
Moscow, along with China, has blocked tougher U.N. Security Council action and the West has shown no appetite for the kind of intervention it undertook last year when NATO helped topple Libya's Muammar Gaddafi.
Annan said on Friday he was "shocked and appalled" at the government for breaking a promise not to use heavy weapons in populated areas, and that it was confirmed that helicopters and artillery had fired on the village of Tremseh.
The Syrian government said it killed several dozen enemy fighters in Tremseh but denied carrying out a massacre or that its forces used heavy weapons.
Syrian Foreign Ministry spokesman Jihad Makdissi criticised Annan for jumping to conclusions by accepting opposition reports of the incident last week.
"Government forces did not use planes, or helicopters, or tanks or artillery," he told a news conference in Damascus. "What happened was not a massacre ... what happened was a military operation."
(Additional reporting by Khaled Oweis; Writing by Mariam Karouny and Erika Solomon)