BEIRUT — Syrian guns pounded rebel positions in Aleppo on Sunday, as panicked residents streamed from the besieged city and the opposition denied the military was driving out insurgents.
The United Nations said more than 200,000 people had fled the city in the last two days. The flight coincides with a military bombardment with artillery and helicopter gunships, the opposition says.
Many districts in the city of more than 2 million have been largely abandoned, witnesses said. Residents left the city or relocated to areas of town away from the fighting.
An unknown number of civilians remained trapped in Aleppo, said the U.N., which appealed to both sides to grant safe access to aid groups.
The battle for the northern city — Syria's commercial hub — could be a decisive moment in the Syrian conflict, which began more than 16 months ago with street protests but soon evolved into an armed rebellion against the government of President Bashar Assad. The United States and other nations have warned of a possible bloodbath in Aleppo, about 200 miles north of Damascus, the Syrian capital.
Syrian authorities vowed Sunday that that the "terrorists" — the official term used by the government for armed rebels — would be vanquished. The official news agency said troops had inflicted "very heavy losses on the terrorists" in Aleppo, while "fleeing terrorists are being pursued and ... their hide-outs are being raided."
The opposition offered a conflicting narrative, asserting that rebels had held off the military assault while inflicting heavy losses on government troops.
Unverified video said to be from Aleppo and uploaded onto the Internet showed refugees fleeing, smoke rising from residential buildings, soldiers firing into city streets and rebels setting up checkpoints, among other images.
Reports Sunday indicated that government forces held back scores of tanks that are said to be massed outside the city, many near a stadium complex in the southwestern district of Hamdania.
Instead of a direct assault with tanks and troops, which are vulnerable on narrow streets, the government may rely on shelling and fire by helicopter gunships. That was the strategy employed this year in the central city of Homs, where weeks of shelling finally forced rebels out of the Baba Amr district and left much of the area in ruins.
"They want to do what they did in Homs," Col. Abduljabbar Aqidi, a rebel commander, told Agence France-Presse in an interview. "The army can only use its aircraft or heavy artillery at a distance, shelling cities, destroying houses. It cannot enter the city."
The opposition appears to have calculated that a counterattack that leaves much of the city in rubble will serve to erode whatever public support remains for the government. Destroying Syria's most populous city looms as a high price for victory in Aleppo, once counted as a bastion of support for Assad.
"Most of the people, and even the middle class, are now with the revolution as they are watching Aleppo being destroyed by the regular army," said one opposition activist speaking from the Firdous district, close to the historic old city.
But press accounts from the city also indicate that some residents are angry at the opposition for having provoked a military onslaught likely to cause widespread devastation.
Unlike the recent fighting in Damascus, where uprisings in scattered districts appeared spontaneous in nature, the rebel assault on Aleppo seems to be based on a plan. It began with a months-long campaign to seize many of the city's suburbs and outskirts, easing the path for infiltration and opening supply routes from the Turkish border.
On July 20, rebels began occupying some of Aleppo's outlying areas, from the southwest to the northeast. The districts appear to have been chosen because their residents, mostly members of Syria's Sunni Muslim majority, were hostile to Assad's government. Members of Assad's minority Alawite sect, an offshoot of Shiite Islam, dominate his administration.
Some of Aleppo's rebel-occupied districts, like Salahuddin and nearby Sikari, both in the city's southeast, are home to people whose family roots are in nearby Idlib province, a hotbed of the insurgency.
Until recent days, Aleppo had largely been insulated from the violence raging in Syria's provinces.
For much of the rebellion, Aleppo's Sunni Muslim merchant class, as well as minority Christian and Kurdish populations, among others, were thought to have remained generally loyal to Assad. Many were wary of the opposition and the possibility of Iraq-style chaos. Some Christians see the rebellion, with its Islamist overtones, as a threat to religious tolerance.
In comments to reporters Sunday, U.S. Defense Secretary Leon E. Panetta said the Syrian government's use of helicopter gunships will prove to be "a nail in Assad's coffin." He spoke at the beginning of a five-day Mideast tour.
Marrouch is a special correspondent. Times staff in Reyhanli, Turkey, contributed to this report.