Syrian forces bombarded three districts of Damascus with helicopter gunships on Sunday, witnesses said, clawing back territory from rebels a week after the fighters launched what they called a final battle for the capital.
Fighting also raged around the main intelligence headquarters in Syria's biggest city, Aleppo — the country's main commercial and industrial hub — and in Deir al-Zor on the Euprhates river, the largest city in the east.
Rebels said they had captured a third border crossing with Turkey on Sunday, Bab al-Salam north of Aleppo, while Iraqi officials said Syrian forces had regained control of one of two border crossings seized by rebels on the frontier with Iraq.
The helicopter bombardments in Damascus and Deir al-Zor showed President Bashar al-Assad's determination to regain control after a bomb killed four members of his high command in the gravest blow in the 16-month-old revolt.
Rebels were driven from Mezze, the diplomatic district of Damascus, residents and opposition activists said, and elite Fourth Division troops were besieging the northern neighbourhood of Barzeh, one of three northern areas hit by helicopter fire.
The fourth division is run by Assad's younger brother, Maher al-Assad, 41, who is widely seen as the muscle maintaining the Assad family's four decades of Alawite minority rule.
His role has become more crucial since Assad's defence 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 public since the bombing. Diplomats and opposition sources said government forces were focusing on strategic centres, with one Western diplomat comparing Assad to a doctor "abandoning the patient's limbs to save the organs."
Syrian state television quoted a media source denying that helicopters had fired on the capital. "The situation in Damascus is normal, but the security forces are pursuing the remnants of the terrorists in some streets," it said.
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 and attacked security installations and roadblocks.
Residents said the sound of shelling in the capital 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 said late on Saturday that helicopters had fired rockets into a neighbourhood near the southerly Sayida Zeinab district, causing dozens of casualties. They did not have any other details.
"In Damascus, people continue to search desperately for safety," the International Committee of the Red Cross (ICRC) said in a statement in Geneva.
"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. The ICRC and the Syrian Arab Red Crescent have intensified their response to the situation."
The Syrian Observatory for Human Rights, an opposition group that monitors the violence, said 180 people, including 48 troops, had been killed across Syria on Saturday. Many of them died in the province of Homs, epicentre of the uprising.
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 Shia Islam, and rebels drawn largely from the Sunni majority.
UN Secretary General Ban Ki-moon said he was sending his peacekeeping chief Herve Ladsous and top military adviser General Babacar Gaye to Syria to assess the situation.
Opposition activists in Aleppo said 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 neighbourhood of al-Sakhour.
"The sound of bombardment has been non-stop since last night. For the first time we feel Aleppo has turned into a battle zone," a housewife, who declined to be named, said by phone from the city.
Rebel border crossing raid
On the Iraqi-Syrian border, Iraqi security and border officials said Syrian forces had reasserted control over the Yarubiya crossing point on the Syrian side 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.
The surge in violence has trapped millions of Syrians, turned sections of Damascus into ghost areas, and sent tens of thousands of refugees fleeing to neighbouring Lebanon.
The UN 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 after Russia and China vetoed a resolution to impose UN 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".
"The Syrian government has manifestly failed to protect civilians and the international community has collective responsibility to live up to the U.N. Charter and act on its principles," he said.
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./p>