Regional relations, always tenuous, have been particularly strained in recent weeks after South Korea agreed that the U.S. could deploy its the Thaad missile system on South Korean soil. Both countries hope the anti-ballistic missile system would deter North Korean leader Kim Jong-un's regime, which since January has increased its missile test launches in the region.
The U.S.-South Korea deal, however, incurred the wrath of neighboring China, which called the Thaad deployment a threat to its national security.
"What is really going on is a deeper political game. By poking the U.S. and South Korea, effectively North Korea is driving a wedge between China, the U.S. and South Korea," Stephan Haggard, director of the Korea-Pacific program at the University of California San Diego, said. "It's actually a quite clever diplomatic gambit that [Kim] is playing."
The U.S. and South Korea also kicked off joint military exercise on the Korean Peninsula on Monday, with 25,000 U.S. troops taking part South Korea's Ulchi Freedom Guardian exercise that runs until September 2, Reuters reported. GPS systems and military aircraft from both countries are being used in the exercises for the first time.
According to Reuters, the U.S.-led U.N. Command Military Armistice Commission said it had notified the North Korean army the exercises were "non-provocative." But North Korea, which views such exercises as preparations for invasion and often responds to them with missile tests, on Monday threatened a preemptive strike.