(AP) BEIRUT - Fighter jets unleashed sonic booms and helicopter gunships strafed rebels as they pressed their fight Tuesday into new neighborhoods in Aleppo, Syria's largest city. Farther south, ground troops combed Damascus after the nearly complete rout of the largest rebel assault yet on the capital.
After a series of setbacks, President Bashar Assad's forces are solidifying their grip on Aleppo and Damascus, knowing that their fall would almost certainly spell the regime's end.
Despite a recent series of high-profile defections, including a close friend of Assad on Tuesday, the regime appears to be regaining momentum after a series of setbacks that put it on the defensive. But while its forces easily outgun the rebels in direct confrontations, the rebellion has spread them thin - pointing to a drawn-out civil war.
Syria's two biggest cities, home to more than one-third of the country's 22 million people and centers of its political and economic life, have remained largely insulated from the unrest that has ravaged much of the rest of the country during the 16-month conflict.
But this month, rebels from surrounding areas have pushed into both, bringing street battles to previously calm urban neighborhoods.
The fighting in each city has followed a similar script.
After building up their forces in the countryside and clashing with government troops there, rebels pressed into Damascus early last week, sparking clashes around the city with government troops.
The opposition landed a harsh blow July 18, when a bomb tore through a high-level security meeting, killing four top Assad security advisers including his minister of defense and his older sister's husband. All had been key architects of the government's efforts to quash the uprising.
But the battle turned when the regime deployed the overwhelming force it has used to crush rebels elsewhere, shelling residential areas and targeting rebels with machine guns and missiles fired from attack helicopters.
On Tuesday, the government appeared to have largely retaken the capital. Activists reported shelling and sporadic clashes between troops and rebels in and around the city, but acknowledged that most fighters had withdrawn.
"They had to withdraw because they lacked ammunition and organization, because the regime was stronger and because they didn't want to hurt civilians," Damascus activist Mohammed Saeed said via Skype.
The fighting took a huge toll, making June one of the deadliest months in a conflict that activists say has killed more than 19,000 people.
About one-third of the 150 people killed across Syria on Monday were in or near Damascus, said the Britain-based Syrian Observatory for Human Rights.
Amateur video posted online Tuesday showed the aftermath: buildings reduced to rubble by government shells, helicopters hovering overhead and columns of smoke rising from areas still on fire.
Other videos showed tanks in the streets and crowds of foot soldiers combing areas once held by rebels.
Syria's state news service said troops chased "armed terrorists" from some districts after killing and wounding many of them and were still searching other areas. Syria blames terrorists backed by foreign powers for the uprising.
Videos and claims could not be independently verified. The Syrian government prevents most media from operating in the country.
While the regime asserted control in the capital, rebels in the north launched an assault on Aleppo over the weekend. They pushed into neighborhoods in the southern and northeastern edges of the city and destroyed at least three government tanks.
The fighting expanded on Tuesday, with clashes spreading into neighborhoods on two sides of the historic old city and into a number of other areas, activists said.
The government fought back much as it did in Damascus, firing artillery shells on rebel areas and pursuing fighters with attack helicopters. Residents also reported fighter jets swooping over the city, breaking the sound barrier to cause sonic booms in a show of force.
"It's the worst day of fighting in Aleppo so far, but I can't tell what's happening on the ground or who's in control," said a local writer who spoke on condition of anonymity for fear of reprisals. "This is bad because in the end it's the civilians who will pay the price of this street fighting."
Prisoners in Aleppo's jail also rioted overnight, and activists said government forces killed at least eight of them. Guards quelled another prison riot in the nearby city of Homs with tear gas and live ammunition.
At least 26 of the more than 110 people killed nationwide on Tuesday died in Aleppo province, the Syrian Observatory said.
Also Tuesday, a top military commander and close friend of Syrian President Bashar Assad confirmed his defection from the regime.
Brig. Gen. Manaf Tlass, son of a former defense minister, said in a video broadcast on Al-Arabiya TV that Syrians must work together to build a new country.
"I speak to you not as an official, but as a son of Syria, as a son of the Syrian Arab army that has rejected the criminal program if this corrupt regime," Tlass said, dressed in a light blue shirt with an open collar, his gray hair tussled.
"Our duty today as Syrians is to unify for one goal, and that is to make our country free and democratic," he said.
It was his first public appearance since he left Syria earlier this month. French officials later confirmed that he was in France.
His long silence raised questions about whether he had joined the anti-Assad uprising or merely fled the civil war.
Tlass is the highest-level defector from the Syrian regime since the conflict's start.
He was a member of the elite Republican Guard and son of former Defense Minister Mustafa Tlass, who served under Assad's father.
Syria's uprising started when political protests in March 2011 met a harsh government crackdown. As dissent spread and the death toll rose, many in the opposition took up arms and the conflict transformed into a civil war.
Syria's position as a geographic and political crossroads for the Middle East and beyond has given its conflict resonance far beyond its borders.
The U.S. and many Western nations have said that Assad must go, while Russia and China have stood by the regime and protected it from international condemnation by the United Nations Security Council.
Iran also counts Assad as a close ally and a bridge to the Lebanese militant group Hezbollah, which it funds and arms. On Tuesday, the commander of the Iran's powerful Revolutionary Guards, Gen. Masoud Jayazeri, warned of retaliation if any Arab countries intervened in Syria.
Despite rising condemnation of Assad, no country appears ready to intervene militarily to push him from power. Still, a Syrian official on Monday threatened that Syria could use chemical or biological weapons if it were attacked from outside.
Russia on Tuesday rebuked Syria for the threat, reminding Damascus that it had ratified a global convention banning the use of chemical weapons. A foreign ministry statement said Syria must "unfailingly honor its international obligations."
(At left, watch CBS Evening News correspondent David Martin's report on the threat posed by Syria's chemical weapons stockpile, reportedly the world's largest.)
In Israel, which shares a closed and hostile border with Syria, the military chief warned his own government that an Israeli attack on Syria's chemical weapons depots could drag the Jewish state into a broader war.
Israeli officials have expressed fears that chaos in Syria could allow non-conventional weapons to reach those who would use them against Israel.
Israel must move cautiously to avoid "a broader offensive than we planned," Lt. Gen. Benny Gantz said, according to the army's website.
It remains unclear if the rebels in Aleppo will hold out longer than their colleagues did in Damascus. But even activists who acknowledged the loss of the capital said a larger battle had been won.
For the first time, the image of Damascus as standing outside of the uprising has been shattered, said Rami Jarrah, head of the Cairo-based Activists News Association.
"If this happened once, it can happen again," he said. "But next time," he said of the rebels, "they'll be more prepared."