(CNN) -- Syrian President Bashar al-Assad's government and the opposition demanded independent investigations Wednesday into countering accusations of the use of chemical weapons, allegations that prompted most members of the U.N. Security Council to call for a probe. The demands, made in writing to the United Nations, came a day after the government and the rebels accused one another of using chemical weapons in fighting in the flashpoint province of Aleppo and a rural suburb of the Syrian capital of Damascus. Even as both sides accused the other of using such weapons, the U.S. ambassador to Syria and other officials said there was no evidence to substantiate the reports.
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NEW: The Security Council asks Ban Ki-moon for a "swift, thorough and impartial" investigation
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U.N. Security Council calls for investigation to "shed light" on chemical weapons claims
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"We have no evidence" to prove chemical weapons use, U.S. ambassador to Syria says
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Medical evidence and satellite imagery are a focus of chemical weapons inquiry, sources say
@placeholder officials pointed to previous claims that the Syrian government used chemical weapons, which were found to be false after extensive investigation.