(CNN) -- For the third straight day, fierce clashes erupted in the Syrian capital Tuesday as fighters braced for a major showdown in the key city, opposition activists said.
"The battle for Damascus is coming," said Abdulhameed Zakaria, a Syrian army colonel who defected and joined the rebel Free Syrian Army.
Several areas of Damascus came under intense fighting early Tuesday, the opposition Local Coordination Committees of Syria said. Mortar shells rained on the Tadamon neighborhood as a powerful explosions rocked Tadamon and other areas, the LCC said.
But the violence wasn't limited to the Syrian regime's seat of power.
Warplanes pummeled the southern city of Herak with shelling, the LCC said, and at least two rockets fell on the city.
Amid the spiraling chaos, U.N.-Arab league special envoy Kofi Annan is set to meet Russian President Vladimir Putin in Moscow on Tuesday.
Russia and China, which have commercial deals with Syria, have used their veto power at the U.N. Security Council to block some of the toughest draft resolutions against the Syrian regime.
Numerous countries, including the United States, have criticized Russia, saying its actions in the Security Council have helped Syrian President Bashar al-Assad's forces to continue a lethal crackdown on dissidents.
On Monday, Russian Foreign Minister Sergey Lavrov slammed Western countries that are trying to change Russia's stance.
"The track record of those who try to make us step aside from this position has a lot of deplorable instances of unilateral military actions, and the results are well remembered by everybody," Lavrov told reporters.
With violence spreading throughout Syria, the Red Cross announced that the conflict is essentially a civil war throughout the country.
The declaration officially applies the Geneva Conventions to violence throughout the country. International humanitarian law now applies "wherever hostilities take place," the organization said Monday.
The Red Cross does not use the general term "civil war," but describes the Syrian crisis as a "noninternational armed conflict." In April, the organization declared such a conflict in Homs, Hama and Idlib, but hostilities have been evident in enough areas that the conflict exists throughout the country, ICRC spokesman Sean Maguire said.
"In theory," he said, the Red Cross announcement could affect prosecutions by the International Criminal Court in the future. However, for the court to look at the situation in Syria, a referral from the U.N. Security Council would be required, Maguire noted.
At least 97 people were killed Monday, the LCC said. The carnage was spread across the country: 30 deaths in Hama, 21 in Homs, 13 in Aleppo, 11 in Damascus, eight in Daraa, seven in Deir Ezzor, four in the Damascus suburbs and three in Idlib, according to the LCC.
CNN cannot confirm details of reported violence because Syria has restricted access to the country by international journalists.
Meanwhile, many nations have expelled Syrian ambassadors, with Morocco becoming the latest to do so Monday. Syria responded by declaring Morocco's ambassador persona non grata.
Since the crisis began in March 2011, the United Nations estimates more than 10,000 people have been killed in the violence; opposition activists say more than 15,000 have died.
Throughout the conflict, al-Assad's government has consistently blamed violence on "armed terrorist groups," and reported on its security forces "martyred" in attacks.