Severe clashes broke out Sunday afternoon and overnight in a number of southern neighborhoods of the capital Damascus, mostly in the neighborhood of Tadamun, in what witnesses said the fiercest fighting to have occurred in the capital since the unrest began last year.

Sounds of gunshots and shelling have reverberated across several nearby neighborhoods of Damascus, as wailing sirens have also been blaring amid thick presence of security patrols in a number of areas.

The state news agency SANA said the government troops were after terrorists and gunmen in the Tadamun area, adding that hefty toll was inflicted on the armed men.

Witnesses said the authorities have launched a combing campaign in a number of southern areas, such as Midan, Zahra and Naher Aisha in addition to Tadamun.

Even though the state news agency spelled no details on specific casualties, pro-government media reports claimed that around 80 gunmen were killed in the clashes. Yet their report could not be independently checked.

Sunday's clashes mark the toughest fight inside the capital, witnessed said.

Many of the residents of Tadamun have fled the fight toward the nearby Yarmouk camp for the Palestinian refugees, who have contributed with mattresses and other necessities to support their neighbors.

Witnesses said schools and mosques were opened in Yarmouk area to receive the fleeing people.

Pro-government media also said that after the army gave the armed groups two days to surrender but the latter rejected, the government troops attacked the hideouts of those gunmen, who have been scrambled by the surprising attack and started setting tires on fire and creating chaos.

It said armed extremists affiliated with al-Qaida were among the armed groups entrenching in that part of the city.

Meantime, the opposition activists' network Local Coordination Committees reported the army shelling on a number of areas, including suburbs of Damascus. They said at least 70 people were killed Sunday.

There has been no independent confirmation of the activists' claim.

While the violence on ground raged on, the International Committee of the Red Cross said Sunday that Syria is now in a state of civil war, according to the Guardian.

Alexis Heeb, an ICRC spokesman in Geneva, said, "Now there are many places in Syria that fulfill requirements to be called a non- international armed conflict, and the situation is fluid and constantly evolving."

"What matters is that humanitarian law applies across the country, and that means civilians and those no longer taking part in the conflict are protected," Heeb added.

The ICRC's announcement came hours after the Syrian foreign ministry spokesman denied the government troops' use of air-force and heavy artilleries in a recent operation in the central town of Traimseh.

Scores of people got killed Thursday in Traimseh, but the circumstances remain murky as both the government and the opposition have been trading accusations over the killing.

The Syrian government said army troops carried out a qualitative operation in the village against armed groups upon the request of the residents, who were terrorized by the gunmen in that area.

In a briefing Sunday, the foreign ministry spokesman, Jihad Makdissi, said what happened in Traimseh Thursday was not a massacre but rather a "military operation between the army forces and armed groups that have slapped against" the six-point plan of the UN special envoy to Syria Kofi Annan.

"What had been said about the use of heavy weapons was baseless, " he said, adding that "what happened wasn't an attack on civilians."

On Saturday, UN observers entered Traimseh and said they found pools of blood in homes and spent bullets, mortars and artillery shells.

However, they said the attack appeared to have targeted specific groups and houses, mainly those of army defectors and activists.

Before entering the village, the mission's chief, Robert Mood, said his team in central Hama province saw helicopter gunships in the area.

The teams re-entered Sunday, but no additional details have been provided about their findings.

The situation in Syria is growing more complicated with the ongoing clashes that are getting more momentum and also the constant division of the super powers and their wrestling over Syria.