BEIRUT — Rebels on Friday pressed their broadest assault yet to drive President Bashar Assad's forces out of Syria's largest city, activists said, with fierce fighting erupting in an Aleppo neighborhood that is home to Kurds, an ethnic minority that has mostly stayed out of the civil war.
In Washington, U.S. Defense Secretary Leon Panetta said intelligence suggests Assad has moved some of Syria's chemical weapons to better secure them. Panetta said the main sites are believed to be secure, though his comments indicated that there are lingering questions about what happened to some of the weapons.
On the diplomatic front, top representatives from Western nations and Middle East allies met Friday at the U.N. to urge Syria's fractured opposition to unite. U.S. Secretary of State Hillary Rodham Clinton told the Friends of Syria group that the U.S. would deliver an additional $15 million in non-lethal aid and $30 million in humanitarian support, on top of more than $175 million already given to political opposition.
Diplomacy has been largely sidelined in the 18-month-old Syria conflict because a key tool — U.N. Security Council action — has been neutralized by vetoes from Assad allies Russia and China.
The military battle for control of the country has also been locked in a stalemate, most visibly in Aleppo, a northern city of 3 million. Since a rebel offensive on Aleppo two months ago, each side has controlled about half of the city and has repeatedly tried — but failed — to capture the rest. Aleppo would be a major strategic prize, giving the victor new momentum.
Late Thursday, rebels forces launched what they said would be a "decisive battle" that by Friday had spread to wide swaths of the city. "The city is witnessing one of the most violent days. All fronts are on fire," Aleppo-based activist Baraa al-Halabi said.
Heavy clashes were reported Friday, with regime troops firing tank and mortar shells, and rebels using heavy machine guns, mortars and rocket-propelled grenades, said Aleppo activist Mohammed Saeed.
Amateur video broadcast by the Arab satellite TV station Al Jazeera showed a group of rebel fighters, identified as a single unit by their white headbands, marching through a rubble-strewn street. Others fired assault rifles from behind barricades of cinder blocks and sandbags.
Syria's state-run news agency SANA confirmed battles in a number of Aleppo districts, reporting that dozens of rebels were killed. The Britain-based Syrian Observatory for Human Rights, an activist group, put the day's death toll in the city at 23.
For the first time, rebel fighters entered one of Aleppo's Kurdish areas, amid conflicting reports about whether some of the local residents fought alongside regime troops or stayed out of the battle.
Since the outbreak of the uprising against Assad in March 2011, Kurds have been split in their loyalties, some siding with the regime while others joined opposition protests.
Syria's state TV said regime forces had help Friday from local residents, a claim also made by the Tawhid Brigade, the largest unit of rebel fighters in the city. However, Rami Abdul-Rahman, the head of the Observatory, and Saeed said Kurdish fighters withdrew from the streets when the fighting began.
Kurds are Syria's largest ethnic majority, making up at least 10 percent of the country's 23 million people. Most live in Syria's northeast, near the border with Turkey, but Aleppo and the capital Damascus also have large Kurdish-dominated neighborhoods.
Since the start of the uprising, both the Syrian government and opposition forces have reached out to the long-marginalized Kurds, whose support could potentially help tip the balance in the conflict. Many in Syria's power elite, including the Assad clan, are Alawites — followers of an offshoot of Shiite Islam — while a majority of Syrians are Sunni Muslims. Christians are another large minority.
Syria's civil war is increasingly tearing apart ethnic and religious communities, putting members of the same group on opposite sides of the conflict, said Fawaz A. Gerges, head of the Middle East Center at the London School of Economics.
"The longer the conflict continues, the more fragmented Syrian communities will be," he said. "This does not bode well for the post-Assad Syria."
Since the regime began bombing from the air a few weeks ago, the number of casualties and the scope of destruction have increased sharply. In one such air attack Friday, a warplane bombed the northern town of Azaz near the Turkish border, killing at least four people, according to the Britain-based Syrian Observatory for Human Rights.
Amateur footage posted by opposition activists showed frantic residents clawing with their hands through the rubble of a bomb-flattened home in Azaz. A dust-covered man climbed out of a crater carved by the blast, cradling a dead toddler in his arms. The child's tiny arms and legs flopped as the man carried the limp body to a pickup truck, as shocked bystanders shouted "God is Great."
Syria imposes tight restrictions on foreign journalists, and the authenticity of such videos cannot be verified independently.
In Geneva, the U.N.'s top human rights body stepped up efforts to gather evidence against members of Assad's regime. The Human Rights Council appointed a renowned U.N. war crimes prosecutor, Carla Del Ponte, to its independent panel probing alleged war crimes in Syria. Such evidence could be used in a future war crimes tribunal hearing — although none is planned so far.
The council also extended the panel's mission, due to expire by the end of September, by another six months. Last week, the investigators submitted a confidential second list of suspected war crimes perpetrators to the U.N. human rights office.
There has also been concern that a desperate Assad could unleash chemical weapons on his opponents. It is widely believed that Syria possesses extensive chemical and biological weapons stockpiles and it has threatened to use them if the country comes under attack.
Panetta, the defense secretary, said Friday that there have been multiple "limited" movements of chemical weapons, but that Syrian officials were relocating the stocks in order to better secure them.
"There has been intelligence that there have been some moves that have taken place. Where exactly that's taken place, we don't know," Panetta told reporters. "I don't have any specific information about the opposition and whether or not they've obtained some of this or how much they've obtained and just exactly what's taken place."
Asked if some of the weapons have fallen into the hands of the rebels or Iran's Revolutionary Guard, Panetta said he has no "firm information to confirm that that's taken place." He said the U.S. has monitored the main sites and determined that they are still secure.
President Barack Obama has said the threat of chemical or biological warfare in Syria is a "red line" for the U.S., and has warned that Washington will not allow the weapons to fall into the wrong hands. He said there would be enormous consequences if the U.S. sees any movement or use of the weapons.
Associated Press writers David Stringer at the United Nations and Lolita C. Baldor in Washington contributed reporting.