Beirut, Lebanon - With tanks and artillery, the Syrian Army pounded opposition strongholds in Aleppo on Saturday, stepping up its barrage on a city that for days has been steeling for an assault, residents and activists said.
It was not clear whether the attack, on the edges of the southwestern Salaheddiin neighborhood, was a limited foray by government troops or the beginning of a broader campaign. Activists and residents said that opposition fighters had repelled the attack and destroyed several tanks, but those claims could not be immediately verified.
A resident of the neighborhood named Mohammed, who did not want to give his last name for fear of government retaliation, said that the assault began at dawn, with the sound of helicopters and a warplane. The shelling began soon after that and lasted for hours, far heavier and closer than in recent days.
"Huge sounds of explosions," he said by telephone. "Three or four bombs at once. Those who didn't leave are hiding in lower floors. Others fled to schools or mosques."
The Syrian Observatory for Human Rights, based in Britain, said that at least 2 opposition fighters and 10 government soldiers had been killed in the early fighting in Salaheddiin and nearby neighborhoods.
On Friday, the top United Nations human rights official, Navi Pillay, warned of an "imminent confrontation" in Aleppo. Her comments in Geneva seemed to crystallize the sense of dread of civilians caught between a military that has shown little restraint and the opposition's armed militias, who are reportedly being joined by bands of foreign fighters.
Saying that she had received unconfirmed reports of "atrocities" during continuing fighting in the suburbs of Damascus, Ms. Pillay spoke of "a discernible pattern." The army, she said, had been surrounding villages and cities and cutting off electricity, water and food, before bombarding the town.
"Then tanks move in, followed by ground forces who proceed door to door and reportedly often summarily execute people they suspect of being opposition fighters," she said, adding that other people were detained. The bodies of some who were killed were often burned or taken away, she said.
Mr. Pillay also cited a growing number of reports of atrocities by opposition fighters, including the torture or execution of prisoners. Adding to a growing chorus of international concern, Russia, which has been among the staunchest allies of President Bashar al-Assad of Syria, voiced its own misgivings about the standoff in Aleppo.
In an interview with the Russian state news agency, Deputy Foreign Minister Gennady Gatilov said: "For us this is not an empty question. There are tens of thousands of our citizens there."
He also indicated that Russia was not opposed to provisions in a draft United Nations resolution calling for Syria to transition to a democracy, but that sanctions remained "unacceptable to us."
Russia's foreign minister, Sergey V. Lavrov, said on Saturday that Western and Arab nations should exert more influence on rebels to stop fighting. Tragedy in Aleppo could be imminent, Mr. Lavrov said, according to Reuters, but he indicated that the rebels would be at least partly to blame.
"Pressure must be put on everyone," Mr. Lavrov said in Sochi, Russia, according to Reuters. "Unfortunately, our Western partners prefer to do something a bit different and essentially, along with some countries neighboring Syria, encourage, support and direct the armed fight against the regime."
On Friday, the International Committee for the Red Cross announced it was withdrawing some of its expatriate workers from Damascus because of fears that their safety was threatened by the escalating violence in the 17-month-old conflict. The announcement came a day after the Syrian Arab Red Crescent suspended its first-aid activities in Aleppo, because of what a spokeswoman said was a "lack of respect" for vehicles and facilities bearing the Red Crescent logo.
A Red Cross spokeswoman, Carla Haddad Mardini, said that the Red Cross was not suspending its activities and that a core team of about 50 staff members would remain.
Activists in Aleppo said Friday that more than a dozen people were killed after a missile fell near a vegetable market in the Ferdoss neighborhood. Majed Abdel Nour, a spokesman for the Shaam News Network in Aleppo, an antigovernment group, reported a "massive exodus" from Ferdoss and said that civilians also fled the nearby neighborhood of Bustan al-Qasr after clashes between rebel fighters and soldiers at two government checkpoints.
"They have nowhere to go, so they stay in the streets or in public gardens," said Abu Raed, a resident and an activist. "What's new today is that the regime started shelling the displaced."
About 30 miles west of Aleppo at a windswept police post near the town of Reyhanli, Turkey, there were few refugees. In the past few weeks, hundreds of Syrian families have made it there, but by midafternoon on Friday, there was just one — a father, mother and two wide-eyed children sitting in the back of a military truck, looking lost. The sound of huge explosions thudded across the mountains. "The army has completely surrounded Aleppo, so the refugees can't make it to the border," one Turkish smuggler said.
At least one government defector did escape. Opposition figures said on Friday that a member of the Syrian Parliament from Aleppo Province had defected and crossed into Turkey. The lawmaker, Ikhlas Badawi, was elected in May to a Parliament that was seen as a rubber stamp for Mr. Assad's Baath Party. The elections were dismissed by opposition figures as a sham. After arriving in Turkey, Ms. Badawi said, "I had no more strength to bear the cruelty," according to Turkey's semiofficial news agency.
The government's opponents, anxious for news of cracks in Mr. Assad's government, have hailed the defections of even minor functionaries. "We will work on helping her and making her feel at ease," said George Sabra, a member of the Syrian National Council, the largest Syrian opposition group. "The regime is isolating patriots."
Among the reports of unrelenting violence across Syria on Friday, the killing of a 6-year-old boy who was trying to leave Syria stood out.
The mother of the boy, Bilal el-Lababidi, told The Associated Press that Syrian troops opened fire on her family as they crossed through farmland toward Jordan's border with Syria.
As the family ran, Bilal broke away from his mother, dashing ahead until he was stopped by a bullet that caught him in the neck.
Reporting was contributed by Dalal Mawad from Beirut; Jeffrey Gettleman and Sebnem Arsu from Reyhanli, Turkey; Andrew Roth from Moscow; Nick Cumming-Bruce from Geneva; and Rick Gladstone from New York.