Clashes break out in Syrian capital after civil war designation raises stakes Shaam News Network via Reuters Syrians demonstrators in the al-Tadamun area in Damascus on Sunday. Editor's note: Image released by the opposition Shaam News Network. By NBC News' Ayman Mohedin and NBCNews.com news services Fighting between opposition and government forces in the Syrian capital Damascus erupted for a second day Monday, activists said, one day after the International Committee for the Red Cross declared the conflict to be a civil war. The decision by the Geneva-based group to label the situation in Syria as a civil war is significant because it means that international humanitarian law now applies throughout the country and attacks by either side on civilians and detainees could constitute war crimes. "We are now talking about a non-international armed conflict in the country," ICRC spokesman Hicham Hassan said. Fierce fighting in capital Monday's fighting was reportedly some of the fiercest to hit Damascus since the 17-month-old revolt against President Bashar al-Assad began. The clashes briefly closed the highway linking the capital with Damascus International Airport to the city's south - an unprecedented development, Mustafa Osso, an activist based in Syria, told The Associated Press. "It seems there is a new strategy to bring the fighting into the center of the capital," Osso said, referring to the rebels who fight under the banner of the Free Syrian Army. The capital used to be safe. This will trouble the regime. Red Cross: Syria conflict is now a civil war Amateur video posted online has shown clouds of black smoke billowing above residential buildings where opposition rebels and government forces battled. The authenticity of the video could not be independently confirmed. The Britain-based Syrian Observatory for Human Rights and Osso said the fighting was concentrated in the districts of Kfar Souseh, Midan and Tadamon. The International Red Cross has declared the conflict in Syria to be a civil war. NBC's Ayman Mohyeldin reports on the significance of the designation. There have been sporadic clashes in Damascus in recent months, although Assad's forces remain firmly in control of the capital. Many of the Damascus suburbs, however, have risen up against the regime, prompting a ferocious response from the military in an attempt to clear out rebel fighters from the towns that ring the capital. The spread of fighting in the capital came as U.N. 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 signaled no change in its position on the conflict before talks with Annan. UN investigates Syria massacre site 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. 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, according to activists who said they expected more casualties from the violence on Monday. Accounts in Syria are difficult to verify because the government has restricted access to international media. Ambassador expelled 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. The Guardian newspaper cited reports Monday that Maj. Gen. Adnan Sillu, the former head of Syria's chemical weapons program, had defected to the opposition. 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. 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 Moammar Gadhafi. Annan said 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 on Thursday. U.N. monitors who managed to enter Tremseh have said that the fighting there did not constitute a massacre, as alleged by opposition activists, but that it could more likely be described as a lopsided flight between the Syrian military on the one side and army defectors and residents who tried to defend the town on the other. 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 criticized 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. NBC News' Ayman Mohedin, Reuters and The Associated Press contributed to this report.