CAIRO — As a group of rebels gathered in an apartment in Aleppo, Syria's largest city, debating the value of the United States' decision to provide them with weapons, government forces nearby began pounding an opposition-held neighborhood.
An older rebel who leads a few dozen fighters on one of the front lines in Aleppo was skeptical. The 40-year-old fighter, who calls himself Abu Zaki, said he would believe that America is helping when he sees the arms in his group's hands, rather than statements and baskets of food.
He said the rebels will not forget those who support them and those who support the regime.
At the same time, he said, he did not understand American fears that arms would go to Al Nusra Front, a rebel group linked to al-Qaida, since it had never attacked Western targets.
A similar debate was set off around the world after the announcement on Thursday that the United States concluded that the forces of the Syrian president, Bashar al-Assad, had used chemical weapons and that President Barack Obama was now prepared to send light arms and ammunition to the rebels. Allies and adversaries of the Syrian president argued whether the decision would help speed the end of the conflict, or serve only to escalate the bloodshed.
The United States says the Syrian government used the nerve agent sarin on two occasions in Aleppo in March and April.
U.S. Ambassador Susan Rice detailed the attacks in a letter to U.N. Secretary-General Ban Ki Moon obtained Friday by the Associated Press.
It said sarin was used in a March 19 attack on the Aleppo suburb of Khan al-Assal and in an April 13 attack on the Aleppo neighborhood of Shaykh Maqsud.
It also said unspecified chemicals, possibly including chemical warfare agents, were used May 14 in an attack on Qasr Abu Samrah and in a May 23 attack on Adra.
However, Ban is opposing the U.S. decision to send arms to the Syrian rebels and says there can be no certainty of chemical weapons use in Syria without an on-the-ground investigation.
Syria refuses to allow U.N. inspectors into the country.
Ban reiterated Friday that there is no military solution to the more than two-year conflict and therefore increasing the flow of arms to either side "would not be helpful."
Assad's allies in Russia and Iran condemned the decision, and the leader of the Lebanese militant group Hezbollah, Hassan Nasrallah, vowed to continue fighting on behalf of the Syrian government "wherever needed."
In a telephone call on Friday, Russian Foreign Minister Sergey V. Lavrov told Secretary of State John Kerry that Washington's allegations about chemical weapons "were not supported by reliable evidence," according to a Russian Foreign Ministry statement. Lavrov said American support for the opposition risked escalation in the region.
The Syrian government said the American reports about chemical weapons use were "full of lies" and paved the way for intervention.
Inside Syria, the news of American aid energized antigovernment activists in Aleppo. The rebels had blasted into Aleppo almost a year ago, eager to occupy the most populous city, which was a commercial center. But the government fought back and the rebels stalled.
Once the government, with Hezbollah's help, managed to rout the rebels from the city of Qusayr, there were fears that the forces would move on Aleppo. It was not clear Friday if the heavy fighting represented the start of an all-out attack, or just another skirmish.
"Now we can say Americans are our real friends, and we will not forget their position and help to finish the Assad regime," said Abdel-Qader, 30, an activist in Aleppo.
A rebel commander, Jamal Maarouf, reached in Aleppo via Skype called the American decision good news but said what the rebels really needed were antitank and antiaircraft missiles.
"The American said they will arm moderate battalions," he said. "I don't know if my battalion is moderate."
Information from the Associated Press was used in this report.