(CNN) -- Infighting between Syrian rebels threatened a hospital in the northern city of Aleppo on Sunday, a source said, forcing doctors to hide patients as clashes flared between Islamists and members of the Free Syrian Army. "Doctors are working neutrally, treating both sides," said the source in northern Syria, who asked to remain anonymous for fear of reprisal attacks. As doctors treat the wounded, fighters from the FSA and the al Qaeda-linked Islamic State of Iraq and Syria, or ISIS, are fighting outside the hospital and plotting to attack each other inside, the source said. The clashes come after the FSA gave ISIS members a 24-hour ultimatum to surrender and leave the country and arrested 200 members of the al Qaeda-linked group.
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Rebels from the Free Syrian Army are clashing with al Qaeda-linked fighters
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Both are fighting to topple al-Assad's government; now, they're fighting each other
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"Doctors are working neutrally, treating both sides," source says
@placeholder issued its own ultimatum on Saturday, giving the FSA 24 hours to free their prisoners, or they will leave their joint posts with the FSA in Aleppo.
"The medical staff in Aleppo will be targeted by ISIS if they know that they are treating FSA patients, by @placeholder if they know that they are treating ISIS patients, and by (the) regime's airstrikes if they know that they are treating both," the source said.