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The Observatory reported a similar attack on Sunday on the town of Tal Rifat, some 20 miles north of Aleppo. There was no immediate word on casualties.

Also Sunday, French freelance photographer Olivier Voisin, who was wounded on Thursday in Syria and taken to Turkey for treatment, died of his wounds at an Istanbul hospital, the French Foreign Ministry said.

Mr. Voisin is the second French journalist this year to be killed while reporting on the civil war, which has proved to be one of the most dangerous conflicts for reporters to cover.

The United Nations says at least 70,000 people have been killed since the uprising against Mr. Assad’s authoritarian rule began nearly two years ago.

Efforts to stop the bloodshed so far have failed, leaving the international community at a loss of how to end the civil war.

A senior opposition leader said Sunday that his umbrella group has suspended participation in meetings with its Western backers and their Arab allies because of their indifference over the regime’s attacks on the Syrian people in Aleppo and other cities.

Assad has reached the stage of real genocide amid Arab silence, and we renounce that,” said George Sabra, vice president of the Syrian National Coalition. He spoke to reporters in Cairo after meeting with Arab League chief Nabil Elaraby.

On Friday, a statement posted on the Facebook page of Mr. Sabra’s opposition group said its leaders would not travel to Washington or Moscow for any talks to protest the international community’s “silence over crimes committed by the regime.”

The statement also said that the opposition leaders would boycott a meeting next month in Rome of the Friends of Syria, which includes the United States and its European allies.

In Washington, the State Department condemned rocket attacks on Aleppo, saying in a statement late Saturday the strikes are the “latest demonstrations of the Syrian regime’s ruthlessness and its lack of compassion for the Syrian people it claims to represent.”

• Associated Press writers Ryan Lucas in Beirut and Lori Hinnant in Paris contributed to this article.