Syrian rebels take the fight to a Kurdish area of Aleppo

BEIRUT, Lebanon - Rebels on Friday pressed their broadest assault yet to drive President Bashar al-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, Defense Secretary Leon E. 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. Secretary of State Hillary Rodham Clinton told the Friends of Syria group that the United States would deliver an additional $15 million in nonlethal 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 three 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.

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-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.

In Geneva, the United Nations' 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.