Syrian government forces early on July 25 fired artillery and rocket barrages into the northern Damascus suburb of al-Tel in an effort to seize the town back from opposition fighters.
The bombardment was causing a mass panic with hundreds of families fleeing the area.
Residents and opposition activists say the Syrian Army's 216th mechanized battalion, which is headquartered near Tel, started bombarding the town of 100,000 people overnight at the rate of one shell or rocket every minute.
Initial reports indicated that residential apartment blocks were being hit.
Tel, located eight kilometers north of Damascus, fell into the hands of rebel fighters last week along with several districts in the capital and on its outskirts after a bomb killed four of President Bashar al-Assad's top security officials.
Government forces early on July 25 also were combing through districts of Damascus that they have retaken from rebels after the near complete rout of the opposition's assault on the capital during the past week.
Meanwhile, in Aleppo, the government was using fighter jets and helicopter gunships to attack several neighborhoods seized by opposition forces in recent days.
A column of armored vehicles and thousands of Syrian Army troops also was advancing on Aleppo early on July 25 after vacating a strategic plateau in the northwestern province of Idlid.
Activists say rebels in the Syria Free Army attacked the tail end of the column overnight as the government troops were advancing toward Aleppo.
On July 24, U.S. Secretary of State Hillary Clinton said opposition fighters were making some territorial gains that eventually could become "safe havens" and provide a base for further rebel operations against government forces.
Clinton also told reporters in Washington that it is not too late for Assad to begin planning for a political transition to end Syria's civil war.
But analysts say appointments made by Assad on July 24 of well-known regime figures to head security and intelligence operations suggest it is unlikely the government would end its efforts to defeat rebel fighters.
The intensified government counter-offensives in Damascus and Aleppo came after a top commander from the Syrian Republican Guard and close friend of Assad confirmed that he had defected from the regime.
Brigadier General Manaf Tlass, the son of former defense minister Mustafa Tlass, said in a video broadcast on Saudi-owned Al-Arabiya TV that Syrians must work together to build a new, democratic country.
He also said members of the Syrian Army should denounce "regime crimes" committed during the government's bloody crackdown on dissent.
Tlass is the highest-level defector from Assad's regime in the 17-month uprising that activists say has left more than 19,000 dead.
The video is his first public appearance since he left Syria earlier in July.
His long silence raised questions about whether he had joined the anti-Assad uprising or merely fled Syria's civil war.
General Tlass did not say where he is. Earlier unconfirmed reports suggested that Tlass fled into Turkey.
Turkey, meanwhile, has announced that border gates with Syria are being closed in response to the violence.
The Associated Press quotes Turkish Customs and Trade Minister Hayati Yazici as saying border gates with Syria will be closed to trucks unless they are travelling on to third countries.
Syrian rebels seized control of several gates on the Syrian side of the frontier over the last week. Reports say refugees from Syria have been crossing into Turkey through smuggling routes.
Elsewhere, Syrian rebels have accused the government of moving chemical weapons to airports near the country's borders. The claim by the opposition Free Syrian Army could not immediately be confirmed.
A government spokesman said Damascus would not use chemical weapons against Syrian citizens but could use them against foreign troops if there is international military intervention in Syria.
Reacting to the statement, U.S. President Barack Obama warned that Assad and his regime would be "held accountable" by the international community and the United States if it used chemical weapons.
Russia criticized the threat, noting that Damascus was bound by international treaties not to use chemical weapons.
With reporting by Reuters, AP and AFP