SINGAPORE—A senior NATO general criticized China’s decision to ignore an upcoming Hague tribunal ruling on Chinese maritime claims, saying that Beijing risks fueling regional instability by unilaterally flouting international norms in dispute resolution.

“Whenever the government of a sovereign country says upfront they would not respect a ruling of the court, it’s not helpful,” Czech Army Gen. Petr Pavel, who chairs the alliance’s military committee, said Friday in an interview. Such behavior “sets the example for others that...