The country's National Coordinator for Security and Counterterrorism said in a statement Wednesday, "The chance of an attack in the Netherlands or against Dutch interests abroad has risen."
The warning comes just two months before hundreds of thousands of people are expected to descend on Amsterdam for the abdication of Queen Beatrix and investiture of her son, Crown Prince Willem-Alexander, as king.
The government cites the threat posed by jihad fighters returning from Syria and signs of increasing radicalization among Dutch youth at home.
Substantial is the second-highest level on the four-step scale, just below "critical."
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