The verdict by the Permanent Court of Arbitration - the world's oldest international tribunal for the peaceful resolution of disputes between nations - could further inflame tensions in an already volatile row over the strategic waterway.
The court in The Hague said in a statement it had informed the parties that it would issue its ruling at about 11am (0900 GMT) on July 12.
The written decision will first be emailed to the parties, and then released to the press and uploaded onto the PCA's website.
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