Syrian forces and their Lebanese Hezbollah allies seized control of the border town of Qusair on Wednesday, dealing a strategic defeat to rebel fighters battling for two years to overthrow President Bashar al-Assad.
Outgunned rebels said they had retreated from Qusair, which lies on a vital cross-border supply route with Lebanon, after two weeks of fierce battles that marked the Shi'ite Hezbollah group's deepest involvement yet in Syria's civil war.
A Hezbollah fighter said the town had fallen in a rapid overnight offensive, allowing tanks and troops to roll into the rubble-strewn streets after dawn, with many buildings in the city centre reduced to mounds of twisted concrete.
"We will not hesitate to crush with an iron fist those who attack us. ... Their fate is surrender or death," the Syrian armed forces command said in statement.
"We will continue our string of victories until we regain every inch of Syrian land."
Hezbollah's Al-Manar television showed a man climbing the bullet-pocked clocktower in the town's wrecked and mangled central square to plant a Syrian flag.
Bolstered by his Iranian and Russian backers, Assad's forces have launched a series of counter-offensives in recent weeks against mainly Sunni Muslim rebels battling to overthrow him and end his minority Alawite family's four-decade grip on power.
A member of a pro-Assad Syrian militia said the military focus may now move to the northern province of Aleppo, which has been largely in rebel hands for the last year.
Assad's upturn in fortunes could further diminish hopes of concessions at a peace conference the United States and Russia are seeking to convene, with Damascus increasingly confident of success against a ragtag opposition that is short of weapons.
Qusair had been in rebel hands for more than a year, denying Assad an important corridor through the central province of Homs which links Damascus to the coastal heartland of Assad's minority Alawite sect, an offshoot of Shi'ite Islam.
"Whoever controls Qusair controls the centre of the country, and whoever controls the centre of the country controls all of Syria," said Syrian Brigadier-General Yahya Suleiman, speaking to Beirut-based Mayadeen television.
More than 80,000 people have been killed since the Syrian revolt erupted in March 2011, and 1.6 million refugees have fled a conflict which has fueled sectarian tensions across the Middle East, spilled over into Lebanon and divided world powers.
US and Russian officials were due to meet the UN-Arab League envoy for Syria, Lakhdar Brahimi, in Geneva later on Wednesday (local time) to discuss plans for the planned peace conference.
Syrian artillery and aircraft had pounded Qusair in recent days and humanitarian agencies warned earlier this week that as many as 1500 wounded were trapped in the town. Their fate was not immediately clear.
The International Committee of the Red Cross said it hoped to gain access to Qusair to deliver food and medical aid to civilians. Syrian authorities had told the ICRC this week that its aid workers could enter once military operations were over.
The rebels said in a statement they had pulled out "in face of this huge arsenal (of pro-Assad forces) and a lack of supplies and the blatant intervention of Hezbollah ... Dozens of fighters stayed behind and ensured the withdrawal of their comrades along with the civilians".
Assad's forces had left an escape route into Debaa and the Lebanese border town of Arsal to encourage rebel fighters to quit Qusair, once home to some 30,000 people, said a security source with ties to Syrian forces.
A rebel commander in contact with the brigades that retreated said the decision to withdraw was taken after a day of rocket fire from the Syrian army and Hezbollah that "levelled what had remained" of Qusair.
"An exit remained open from the north and the fighters took a decision to leave from there."
In the Hezbollah stronghold of southern Beirut, residents set off celebratory fireworks as news of Qusair's fall spread.
In the Lebanese town of Qasr close to Syria, crowds waved Hezbollah and Syrian flags in jubilation. Locals distributed sweets to mark the rebel defeat just across the border.
A senior Lebanese political source close to Hezbollah said the victory was a strategic success that would boost the morale of Assad's allies. He suggested that Hezbollah would not necessarily intervene directly in other battles but might offer indirect help to the Syrian army.
"The battle will continue in all regions, but I believe Aleppo (will be) first," he said.
Underlining a possible further spillover of the conflict into Lebanon, the commander of the rebel Free Syria Army warned that it might target Hezbollah on its home turf.
"Hezbollah fighters are invading Syrian territory. And when they continue to do that and the Lebanese authorities don't take any action to stop them coming to Syria, I think we are allowed to fight Hezbollah fighters inside (Lebanese) territory," Salim Idriss told the BBC.