North Korean leader Kim Jong Un visits the Kwisong Saltern to learn about the salt production from underground ultrasaline water by the KPA in this undated photo released by North Korea's Korean Central News Agency, on May 24, 2016. Reuters

A North Korean patrol boat and fishing boat crossed into disputed territory off the Korean peninsula Friday, prompting South Korea's navy to fire warning shots in the latest sign of escalation between the warring nations. The vessels retreated after just eight minutes after the South fired five 40mm artillery shots at around 7:30 a.m. local time, and there were no injuries reported, according to Reuters and the Associated Press.

North Korea disputes the Northern Limit Line border near the South Korean border island Yeonpyeong, and North Korean fishing boats often end up in South Korean waters, resulting in sometimes deadly attacks from both sides, such as when 46 South Korean sailors died when their ship sank in 2010 after a torpedo attack from the North.

North and South Korea have been at a state of war since the Korean War ended in 1953, and the South has been reluctant to engage in so-called peace talks unless Pyongyang ends its nuclear program. North Korea carried out its fourth nuclear test in January. After the South and the U.S. held annual military drills in March, North Korea issued a warning that it would turn its enemies into “seas in flames and ashes."

While North Korea doesn't have the military prowess to take on Washington, analysts have warned that its unpredictable leader, Kim Jong Un, could eventually act on his many threats to the U.S. and its allies.

"North Korea is so poorly understood by outsiders, even by analysts in the South, that its threats make the already jittery Korean Peninsula even tenser. This general anxiety causes both Korean militaries to bolster their positions and increases the possibility that a misjudgment by North Korea’s young leader, Kim Jong Un, could lead to an escalation of violence should a skirmish erupt," the Associated Press wrote in March.