PARIS - Foreign Islamists intent on turning Syria into an autocratic theocracy have swollen the ranks of rebels fighting to topple President Bashar al-Assad and think they are waging a "holy war", a French surgeon who treated fighters in Aleppo has said.

Jacques Beres, co-founder of medical charity Medecins Sans Frontieres, returned from Syria on Friday evening after spending two weeks working clandestinely in a hospital in the besieged northern Syrian city.

In an interview with Reuters in his central Paris apartment on Saturday, the 71-year-old said that contrary to his previous visits to Homs and Idlib earlier this year about 60 percent of those he had treated this time had been rebel fighters and that at least half of them had been non-Syrian.

"It's really something strange to see. They are directly saying that they aren't interested in Bashar Assad's fall, but are thinking about how to take power afterwards and set up an Islamic state with sharia law to become part of the world Emirate," the doctor said.

The foreign jihadists included young Frenchmen who said they were inspired by Mohammed Merah, a self-styled Islamist militant from Toulouse, who killed seven people in March in the name of al-Qaida.

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