BEIRUT/AMMAN (Reuters) - Syrian forces bombarded parts of Damascus with helicopter gunships on Sunday, witnesses said, clawing back territory from the rebels a week after the fighters launched what they called a final battle for the capital.
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 demoralises 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."
The 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 blow 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 armoured 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 said.
"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."
The neighbourhood of Barzeh, one of three northern areas hit by helicopter fire, was also under siege, by troops from the elite fourth division.
The 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 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, attacking security installations and roadblocks.
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 said 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 said late on Saturday that helicopters had fired rockets into a neighbourhood near the southerly Sayida Zeinab district, causing dozens of casualties.
The 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 neighbourhoods in search of safe haven," it said.
The 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
A total of 180 people, including 48 troops, died on Saturday alone, many them in Homs province, epicentre 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.
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 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.
"For the first time we feel Aleppo has turned into a battle zone," a woman, who declined to be named, said by phone from the city.
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 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 after 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.
Additional reporting by Oliver Holmes in Beirut, Igor Ilic in Brijuni, Croatia; Suleiman al-Khalidi in Hacipasa, Turkey; Leigh Thomas in Paris; Jamal al-Badrani in Mosul, Ira; and Jonathan Burch in Cilvegozu, Turkey; Writing by Philippa Fletcher; Editing by Giles Elgood