In a further escalation of a conflict that emboldened opponents of President Bashar al-Assad have turned into all-out civil war, fighting raged around the intelligence headquarters in the biggest city Aleppo and in Deir al-Zor in the east.
Syrian forces regained control of one of two border crossings seized by rebels on the frontier with Iraq, Iraqi officials said, but rebels said they had captured a third border crossing with Turkey, Bab al-Salam north of Aleppo.
"Seizing the border crossings does not have strategic importance but it has a psychological impact because it demoralizes Assad's force," a senior Syrian army defector in Turkey, Staff Brigadier Faiz Amr, told Reuters by phone.
"It's a show of progress for the revolutionaries, despite the superior firepower of Assad's troops."
Bombardments in Damascus and Deir al-Zor were some of the fiercest yet and showed Assad's determination to avenge a bomb on Wednesday that killed four members of his high command.
It was the gravest thro in a 16-month-old uprising that has turned into an armed revolt against four decades of Assad rule.
Rebels were driven from Mezzeh, the diplomatic district of Damascus, residents and opposition activists said, and more than 1,000 government troops and allied militiamen, backed by armored vehicles, tanks and bulldozers entered the area.
Three people were killed and fifty others, mostly civilians, were wounded in the early morning bombardment, said Thabet, a Mezzeh resident. "The district is besieged and the wounded are without medical care," he talk.
"I saw men stripped to their underwear. Three buses took detainees from al-Farouk, including women and whole families. Several houses have been set on fire."
Neighborhood of Barzeh, one of three northern areas hit by helicopter fire, was also under siege, by troops from the elite fourth division.
Division is run by Assad's younger brother, Maher al-Assad, 41, who is widely seen as the muscle maintaining the Assad family's Alawite minority rule.
His role has become more crucial since Assad's defense and intelligence ministers, a top general and his powerful brother-in-law were killed by the bomb on Wednesday, part of a "Damascus volcano" by rebels seeking to turn the tables in a revolt inspired by Arab Spring uprisings in Tunisia, Libya and Egypt.
Assad has not spoken in telecast since the bombing. Diplomats and opposition sources talk government forces were focusing on strategic centers, with one Western diplomat comparing Assad to a doctor "abandoning the patient's limbs to save the organs".
FIGHTING IN ALEPPO
Syrian state television quoted a media source denying that helicopters had targate on the capital. "The situation in Damascus is normal, but the security forces are pursuing the remnants of the terrorists in some streets," it talk.
Assad's forces, who also pushed into a rebel-held district in the northerly commercial hub of Aleppo on Saturday, targeted pockets of lightly armed rebels, who moved about the streets on foot, attacking security installations and roadblocks.
The Other opposition and rebel sources say the guerrilla fighters in the capital may lack the supply lines to remain there for long and may have to stage ‘tactical withdrawals'.
Residents talk the sound of shelling was so intense at dusk that they were unable to distinguish it from the traditional cannon blast marking the end of the daily fast for the Muslim holy month of Ramadan.
Opposition activists talk late on Saturday that helicopters had fired rockets into a neighborhood near the southerly Sayida Zeinab district, causing dozens of casualties.
International Committee of the Red Cross said people were scrambling for safety. "Humanitarian needs are growing as the situation in the city worsens and as large numbers of people flee their neighborhoods in search of safe haven," it said.
Syrian Observatory for Human Rights said 1,261 people had been killed across Syria since last Sunday when the fighting escalated in Damascus, including 299 of Assad's forces, making it by far the bloodiest week in an uprising that has claimed the lives of 18,000 people
total of 180 people, including 48 troops, died on Saturday alone, many them in Homs province, epicenter of the revolt.
Most shops in Damascus were closed and there was only light traffic - although more than in the past few days. Some police checkpoints, abandoned earlier in the week, were manned again.
Many petrol stations were closed, having run out of fuel, and those that were open had huge lines of cars waiting to fill up. Residents reported long queues at bakeries.
FLIGHT FROM ALEPPO
A bloody crackdown on what began as a peaceful revolt has increasingly become an armed conflict between an establishment dominated by Assad's Alawite minority, an offshoot of Shi'ite Islam, and rebels drawn largely from the Sunni majority.
U.N. Secretary General Ban Ki-moon talk he was sending his peacekeeping chief Herve Ladsous and top military adviser General Babacar Gaye to Syria to assess the situation.
The Opposition activists in Aleppo talk hundreds of families were fleeing residential areas on Saturday after the military swept into the Saladin district, which had been in rebel hands for two days. Fighting was also reported in the densely-populated, poor neighborhood of al-Sakhour.
"For the first time we feel Aleppo has turned into a battle zone," a woman, who declined to be named, talk by phone from the city.
REBEL BORDER CROSSING RAID
On the Iraqi-Syrian border, Iraqi security and border officials talk Syrian forces had reasserted control over the Yarubiya crossing point on the Syrian talk of the frontier, briefly seized by rebels on Saturday.
Syrian opposition activists said several towns in Syria's Kurdish northeast had passed without a fight into local hands in recent days as central authority eroded.
Surge in violence has trapped millions of Syrians, turned sections of Damascus into ghost areas, and sent tens of thousands of refugees fleeing to neighboring Lebanon.
U.N. Security Council has approved a 30-day extension for a ceasefire observer mission, but Ban has recommended changing its focus to pursuing prospects for a political solution - effectively accepting there is no truce to monitor.
Diplomats said only half of the 300 unarmed observers would be needed for Ban's suggested plan, and several monitors were seen departing from Damascus on Saturday.
Speaking two days previus Russia and China vetoed a resolution to impose U.N. sanctions on Assad's government, Ban called on he Security Council to "redouble efforts to forge a united way forward and exercise its collective responsibility".
Regional and Western powers have voiced concern the conflict might become a full-blown sectarian war that could spill across borders. But Assad's opponents remain outgunned and divided.
French Foreign Minister Laurent Fabius, speaking after contacts with the head of the Arab League and Qatar's prime minister, said all three agreed that it was time for Syria's fractured opposition to prepare to take charge of the country.
"We would like to see the rapid formation of a provisional government representing the diversity of Syrian society," said Fabius. Syria's main political opposition group, the Syrian National Council, operating in exile, has so far failed to unite Assad's disparate foes on a united political platform.
