BEIRUT – Fighting over Syria’s largest city of Aleppo intensified Friday, with the most widespread battles reported there in two months as rebel forces launched a new offensive to rout President Bashar Assad’s forces, activists said.

Some of the heaviest fighting erupted in a predominantly Kurdish neighborhood, which was drawn into the conflict for the first time. Kurds make up Syria’s largest minority and have been split in their loyalties.

Since the uprising against Assad began 18 months ago, some Kurds have sided with the rebels while others have supported the regime. Aleppo’s Sheikh Maksoud neighborhood is mostly under the control of a pro-government Kurdish group.

Aleppo, once a bastion of support for Assad, has emerged as a key battleground in Syria’s civil war. Its fall would give the opposition a major victory. A rebel defeat would at least buy the regime more time.

In the diplomatic arena, Secretary of State Hillary Clinton on Friday announced $45 million in additional aid for Syrian opposition activists, the latest U.S. push for influence in a civil war that’s raged beyond the international community’s control.

Clinton announced the aid before meeting with visiting Syrian dissidents on the margins of this week’s U.N. General Assembly, where leaders sounded bleaker than ever about the prospects for a negotiated political resolution to the 18-month uprising against Assad.

U.S. humanitarian aid for Syria now will total more than $132 million this year, although Syrian rebels are more interested in weapons and military training than in the American promises of more “nonlethal assistance.” Of the $45 million pledged Friday, $30 million is earmarked for humanitarian assistance and $15 million for radios, training and other technical support for opposition activists.

The U.S. government has refused to directly arm or fund the so-called Free Syrian Army, a loose confederation of rebel militias, largely out of fear that the assistance would make its way to Islamist extremist groups that have joined the battle to unseat Assad.

U.S. policy is in a “really tough spot,” said Joseph Holliday, a researcher at the Institute for the Study of War who specializes in the Syrian conflict. While the administration’s instinct to withhold direct aid from rebel fighters is understandable, he said, that strategy is backfiring.

“The irony of our fear of supplying Islamist groups is that the others who are arming the opposition — the Saudis, the Qataris, the Turks — are doing just that, providing weapons and ammunition to Islamists,” he said. “Our lack of giving support is actually leading to the Islamicization of the opposition.”