SAN FRANCISCO (CBS / AP) — Amid mounting fears of a massacre in Syria’s largest city, the highest-ranking U.S. military official said military intervention is not imminent.

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, told reporters in San Francisco on Friday that the U.S. has no immediate plans for combat in Syria.

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Dempsey says circumstances in Syria are different than Libya, with more competing factions and no UN mandate. The military chief says U.S. military action is more likely if the international community, especially other Arab states, are willing to join.

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The uprising against Syria’s President Bashar Assad reached the commercial hub of Aleppo this week. Troops are bombarding the city with artillery and aircraft.

The Syrian Observatory for Human Rights estimates at least 145 civilians and rebels have been killed in Aleppo.

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