Fabius said yesterday the coalition should not battle IS to the exclusion of supporting rebels fighting President Bashar al-Assad's regime, which he said had deliberately fuelled the jihadists' rise.
"After Kobane, we must save Aleppo," Fabius said, referring to a Syrian border town where Washington has carried out dozens of air strikes with the support of Arab allies to help Kurdish forces ward off a weeks-long IS assault.
France is involved in strikes against IS militants in Iraq but has so far kept out of the air campaign in neighbouring Syria, where it has hoped to support moderate rebels without resorting to military action that could help the Assad regime.
"The regime is seeking to destroy the resistance through cold and hunger," he said in an article published by The Washington Post, France's Le Figaro and pan-Arab daily Al-Hayat.
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"Some 300,000 Aleppans are holding on, threatened with the same death and destruction that the regime has inflicted on Homs and the suburbs of Damascus."
Rebels seized most of the east of Aleppo in July 2012, confining government forces to the west, but they have come under renewed assault in recent months.
"Assad and Daesh are two sides of the same barbaric coin," Fabius said, using the Arabic acronym for IS.
Fabius said France would not resign itself to the breakup of Syria and would work towards supporting moderate rebels in Aleppo and protecting its civilian population, without detailing how.
"Abandoning Aleppo would mean condemning Syria to years of violence. It would mean the death of any political future," he wrote.
His article echoed the words of French President Francois Hollande on Friday, who described Aleppo as "key" to the conflict.