Syrian and Rebel Forces Claim Gains in Nation’s Largest City

In a school transformed into a base, a rebel commander sat at a small desk, drinking tea as updates came over a walkie-talkie. His fighters were on the front lines, watching government troops who had massed around the city. An AK-47 sat on the desk, because the fighting, for the moment, had stopped.

The Syrian Army has descended on Aleppo, with troops, tanks, helicopters and warplanes, hoping to rout hundreds and perhaps thousands of armed opposition fighters who have grabbed a tenuous foothold here.

The battle in Aleppo, Syria’s largest city, could signify a decisive moment in the 17-month-old conflict, proving the government’s resilience or exposing its fragility. The Syrian government, which successfully stopped most rebel attacks on Damascus last week, has promised to make quick work of its opponents in Aleppo.

On Sunday, the rebel commander, Abu Mohammed, who is from Aleppo, boasted of other plans. “We are preparing ourselves for a long, hard guerrilla war,” he said, as he ordered his men to organize night patrols in Salaheddiin, the district at the center of the fighting. “The regime says the war on Aleppo will be ‘the mother of all battles,’ and that they will finish it quickly. But we say, the fighting will be long.”

For most of the uprising, Aleppo, the country’s vital commercial heart, was comparatively quiet, as its merchant class threw its lot in with the government, or remained leery of taking sides. The uprising against President Bashar al-Assad flared here occasionally, in student protests that the government stamped out quickly.

Mr. Assad’s opponents targeted their enemies in the city, and ambushed army soldiers on its outskirts. But full-fledged combat was largely centered elsewhere.

Ten days ago, the city was thrust forcefully into the war as rebels, including defected soldiers organized under the banner of the Free Syrian Army, charged into the city from the surrounding countryside, joining local fighters. They embedded themselves in neighborhoods, and quickly clashed with government soldiers in Salaheddiin and other districts.

Now the city is transformed, its gardens and schools bursting with displaced residents. Its hospitals are filled with civilians wounded during clashes or by the government’s incessant, random shelling. New boundaries have emerged, as the army and its foes delineate their territory with tanks or burned cars.

On Monday, the government and its opponents both claimed victories here. Opposition fighters said that after a pitched battle lasting several hours, they had seized control of a vital checkpoint northwest of the city, in Anadan, freeing up a route for supplies and fighters between Aleppo and the Turkish border. In the fight, the rebels seized several tanks and other military vehicles, activists said.

But with Syrian warplanes and helicopters controlling the skies, it seemed doubtful that the rebels could hold the position. At the same time, Syrian state television reported that the army had won back control of Salaheddiin — vanquishing the “mercenary gunmen,” as one soldier put it. By nightfall, though, clashes in the district raised doubt about that claim.

The combat came as the Syrian government suffered another high-ranking defection from its diplomatic corps, the fourth since the uprising against Mr. Assad began in March 2011. Britain’s Foreign Office announced that the Syrian chargé d’affaires, Khaled al-Ayoubi, the top Syrian diplomatic representative in Britain, had resigned because “he is no longer willing to represent a regime that has committed such violent and oppressive acts.” Diplomats from Iraq, Cyprus and the United Arab Emirates have also defected in recent weeks.

At the United Nations, Secretary General Ban Ki-moon said Monday that the reduced team of monitors had been targeted twice in armed attacks, including an assault Sunday on a convoy led by the new commander. No one in the armored vehicles was hurt.

Mr. Ban also said that he and Kofi Annan, the special envoy to Syria, were “deeply concerned about the situation in Aleppo” and what he called the Syrian military’s use of “all kinds of heavy weapons, including airplanes.”

President Obama, in a phone call with Prime Minister Recep Tayyip Erdogan of Turkey, expressed “growing concerns about the Syrian regime’s ruthless attacks against its own people, most recently in Aleppo,” according to a statement from the White House. The two leaders spoke about how to “coordinate efforts to accelerate a political transition in Syria,” the statement said, without elaborating on those efforts.

On the road to Aleppo, near the devastated city of Homs, the war raced up the road, in buses that ferried soldiers and trucks that hauled tanks. Less than a hundred miles further, the war lingered, on the side of the highway, in the carcasses of military trucks and armored vehicles.

The destruction was evidence of an early attempt by the rebels to stop the army from advancing on Aleppo. Rebel commanders said they either control many of the roads around Aleppo, or have the ability to attack the city’s approaches. The government has increasingly been forced to rely on the airport, which it still controls, opposition activists said. That has not stopped tanks from advancing on the city.

Clashes have occurred in the impoverished, informal neighborhoods on Aleppo’s outskirts, where the rebels have found willing supporters, and in the central districts of the ancient city. Still outgunned, the rebels nonetheless have managed to capture heavier weapons, including tanks and antiaircraft guns mounted on the backs of trucks.

Electricity and water have been cut to many neighborhoods. Most bakeries are closed. The United Nations humanitarian chief, Valerie Amos, said Sunday that 200,000 people had fled the city. Those unable to leave have settled in parks, in Kurdish and Christian neighborhoods that have been spared most of the fighting.

At one of the city’s state-run hospitals, the wards were overflowing with patients wounded in the fighting. Some sat in chairs, and others waited on the ground for treatment, though most of the doctors had not been able to show up for work.

“The ambulances cannot move in the city,” he added. “We have no blood donors. We have no blood bags. The government doesn’t reply to our calls to supply us with more medical staff and equipment.”

The fighters seek treatment at field hospitals, fearing informers and state security officers in the government hospitals. “For the regime, each injured male is a terrorist,” said a volunteer doctor in one of the field hospitals. He said they were bracing for a flood of people, as the state health system faltered.

“We are working hard, to keep these field hospitals away from Assad’s security, and the army’s eyes,” he said.