China has told other Asian countries that it may leave the U.N. Convention on the Law of the Sea as a countermeasure if a ruling from an international tribunal expected in the coming weeks over territorial rows in the South China Sea runs counter to the bedrock of its position, diplomatic sources said Monday.

What China cares most about in an arbitration case brought by the Philippines is a decision on the applicability of Beijing's "nine-dash line" that ambiguously demarcates its claims to almost the entire disputed sea.

The Philippines, the most vocal critic of China's activities in the South China Sea among claimants, filed the case with the Permanent Court of Arbitration in The Hague in 2013 in a bid to invalidate the vaguely drawn territorial line.