BEIRUT: Intense fighting broke out in the capital Damascus Sunday on the eve of a visit by international peace envoy Kofi Annan to Russia where he hopes to lobby support for tougher action at the United Nations to end the violence in the country. Activists reported Syrian army fired mortar rounds into several of the city’s southern suburbs. Fighting also erupted between rebel fighters and President Bashar Assad’s troops in Tadamon, Kafr Souseh, Nahr Aisha and Sidi Qadad.

Activists’ images uploaded to social networking sites showed black smoke billowing over the Damascus skyline of the Tadamon area, within sight of the landmark Four Seasons hotel. Residents said they could hear loud explosions, persistent gunfire and sirens.

“I can’t believe it, it sounds incredibly close. I hear shooting and other stuff, like blasts. I can hear the sounds of ambulances rushing past. I am so afraid. People may die tonight,” said a resident in a district close to the fighting, contacted by telephone.

Residents trying to flee Tadamon, where clashes erupted overnight Saturday, clogged roads out of the city and clashes briefly closed the southern airport road.

Activist Samir al-Shami, who spoke to Reuters by Skype from Damascus, said fighting in Tadamon was the most intense heard in the capital, and added that the clashes followed a night of sustained battles in the nearby Hajar al-Aswad district.

“There is the sound of heavy gunfire. And there is smoke rising from the area. There are already some wounded and residents are trying to flee the area,” he said.

“This area has had a lot of fighting ... The area is kind of a slum. The people who live there are poor. There’s a lot of people and a lot of grassy areas around it so it’s easy for rebels to sneak in and out,” he said.

Other activists said residents were attempting to set up road blocks to prevent security forces, including tanks and armored vehicles, from entering the area.

Meanwhile, later in the evening the fighting spread to Al-Lawan, a neighborhood on the southwestern outskirts of Damascus.

“There are hundreds of fighters in Damascus right now; we’ll see what happens,” said an activist in the capital reached by Skype, who asked not to be named. “If the regime is able to crush the fighters in Tadamon the clashes should stop, but if not they may spread further.”

Earlier in the day an explosion hit a security forces bus in the capital, wounding several people, activists said. Residents said they heard a powerful blast, followed by the sirens of ambulances rushing toward Damascus’ southern ring road near the neighborhood of Midan.

Fighting reached the outskirts of the capital in recent weeks, focusing on poorer areas where anger against the authorities is highest. The past week saw mortars fired inside the capital for what appeared to be the first time.

Clashes have taken place at night with increasing frequency, while intensive battles during the day appear to be a new sign of the seriousness of the conflict.

The opposition monitoring group, the Syrian Observatory for Human Rights, said Sunday’s death toll across the country was at least 80. Rockets were being used in the fighting in Damascus, it said.

“The sounds of explosions and heavy gunfire are still heard in the Tadamon neighborhood, the Sidi Qadad area and Al-Qazaz in Damascus,” it said. “There are violent clashes between regime forces and fighters from rebel battalions in these areas. Ambulances were seen transporting members of regime forces out. These clashes are the most violent to happen inside the capital Damascus.”

Government shelling was also reported elsewhere in the country. A girl died along with three other people when the army rained shells on the town of Rastan, a rebel stronghold in the central province of Homs. Activists said neighborhoods in Hama have been shelled for days.

The government restricts access to the country by independent media and accounts of the violence are hard to verify. Illustrating that difficulty, conflicting accounts of a reported massacre in the village of Tremseh emerged Friday.

The killing of up to 220 people brought a wave of new denunciations of Assad in the West. U.N. observers returned Sunday to Tremseh to gather more evidence at the site after finding blood, damaged houses and signs that artillery was used, but inconclusive evidence of the scale of the killing.

Annan had 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 in Tremseh.

The government, however, said it killed several dozen enemy fighters in a battle in Tremseh, but denied accusations that it carried out a massacre or that its forces used heavy weapons.

Syrian Foreign Ministry spokesman Jihad Makdessi criticized Annan for jumping to conclusions by accepting opposition reports of the incident last week.

“What happened was not a massacre ... what happened was a military operation,” Makdessi told a news conference in Damascus. “Government forces did not use planes, or helicopters, or tanks or artillery.”

He said accusations of a fierce attack were implausible given the tiny size of the village.

“Everything that has been said on the use of heavy weapons in an assault on a village no bigger than 1 kilometer squared is completely untrue,” he said, denying that villagers were targeted. “We are in a state of self-defense, not a state of attack.”

Makdessi also responded to reports on the desertion of Manaf Tlass, a member of Assad’s inner circle, saying he “left without permission.” It was the first time the government acknowledged the disappearance, but Makdessi made no mention of speculation that Tlass had defected to the opposition.

Annan is scheduled to fly to Moscow Monday for a two-day visit in which he will meet President Vladimir Putin.

Western countries have repeatedly suggested they see Putin easing his support for Assad, but Moscow has shown no public sign of wavering in its backing for its last major Arab ally, a customer for its arms and host to a Russian naval support base. A Russian ship tried to supply attack helicopters to Syria last month before being forced back. On Sunday, the ship was sighted sailing back home after unexpectedly starting a new voyage.

Russia and China say they support the peace plan by Annan, which calls for a cease-fire and a negotiated transition to democracy but makes no explicit call for Assad to leave power. Assad’s opponents say negotiations are impossible unless he is removed.

U.N. leader Ban Ki-moon Saturday appealed to China’s foreign minister to use his “influence” to help bring pressure on Assad to end the conflict, a U.N. spokesman said. Ban and Foreign Minister Yang Jiechi discussed Syria in telephone talks ahead of the U.N. secretary-general’s visit to China Monday, said U.N. spokesman Martin Nesirky.

Iran, meanwhile, repeated a long-standing offer Sunday to act as a mediator between the government and opposition, but was immediately rebuffed by opposition activists.