The emir of Qatar has called for an Arab intervention in Syria and a no-fly zone to protect refugees as President Bashar al-Assad's forces stepped up the battle for Aleppo.
More than 100 civilians were killed Tuesday in intense fighting across Syria, activists said, as US President Barack Obama and other Western leaders at the UN General Assembly stepped up calls for an end to Assad's rule.
Qatar's emir, Sheikh Hamad bin Khalifa Al-Thani, urged Arab action in the war-torn state because of the failure of the UN Security Council and other international efforts to end the 18-month-old conflict.
"It is better for Arab countries themselves to intervene out of their humanitarian, political and military duties and do what is necessary to stop the bloodshed," Sheikh Hamad told the General Assembly.
Earlier, Qatar's prime minister, Sheikh Hamad bin Jassem al-Thani, told CNN television that there was a "Plan B" for Syria.
"You need to make safe haven areas, first of all," he said. "That would require a no-fly zone.
"If the Syrians want to break that, that's another subject. We need somebody to have the teeth to tell them 'don't do that', because that will not be allowed."
French President Francois Hollande said the United Nations should protect "liberated zones" under opposition control to help civilians and refugees.
On the battlefield, government forces said they had retaken the Aleppo rebel district of Arkoub. Security forces were conducting door-to-door raids to hunt rebels, a military official told AFP.
Syrian television aired footage of soldiers patrolling Arkoub, where high-rise buildings were shelled out and rubble lined the streets.
The Syrian Observatory for Human Rights insisted that clashes in Arkoub had not ceased and an AFP correspondent heard machinegun fire in the area.
The observatory said at least 114 people had been killed. Activists say more than 29,000 have died since an uprising against Assad started in March 2011.
At the UN assembly, UN leader Ban Ki-moon called on the Security Council to "solidly and concretely" support the peace efforts of UN-Arab League peace envoy Lakhdar Brahimi, who has stated there will be no quick solution.
The 15-nation council is hopelessly deadlocked, with Russia and China resisting international action on the war.
Obama, meanwhile, delivered a blistering attack on Assad in his speech to the UN assembly. "The future must not belong to a dictator who massacres his people," said the US president.
"As we meet here, we again declare that the regime of Bashar al-Assad must come to an end so that the suffering of the Syrian people can stop, and a new dawn can begin."
A State Department official later told AFP that the United States is set to unveil more aid for the Syrian opposition this week, but stressed the supplies will still not include weapons or ammunition.
"We've been clear about our assistance and the type of assistance we are providing and that is going to continue," the official said, after Secretary of State Hillary Clinton met peace envoy Brahimi.
Hollande joined the clamor for Assad to leave. "The Syrian regime will not retake its place in the concert of nations. It has no future among us," he told the assembly.
Aid agencies say there is a mounting humanitarian crisis with more than 2.5 million people now needing help in the country.
Save the Children released a poignant account of the suffering of Syrian children who are being "badly traumatized" after witnessing killing and experiencing torture.
The report "Untold Atrocities" gives first-hand accounts from children and parents who fled the violence, and contains graphic details of how youths have been caught up in the war.
Alongside its publication, explosions shook the headquarters of an army administration building in Damascus which manages schools for children and martyred soldiers. State media said seven people were wounded.
"The explosions were so powerful that the walls collapsed," Observatory director Rami Abdel Rahman told AFP.
Reports from the battlefield said, meanwhile, that regime defector Colonel Kassem Saadeddine, a Free Syrian Army commander in the central province of Homs, escaped an assassination attempt on Tuesday.
Saadeddine's convoy was ambushed by pro-regime militia in Salmiyeh, Hama province, free army spokesman Fahd al-Masri told AFP.