South Korea's president warned the North on Monday that military provocations would be met with a "strong response."
"If there is any provocation against South Korea and its people, there should be a strong response in initial combat without any political considerations," President Park Geun-hye told defense and security officials.
Tensions on the divided Korean Peninsula have continued to rise with Pyongyang's daily bellicose rhetoric amid ongoing joint US-South Korean military exercises.
On Sunday, the US sent F-22 stealth fighter jets to join the drills, while it had already deployed B-2 stealth bombers over the Korean Peninsula in a practice run.
On Saturday, the North declared it was now in a "state of war" with the South, and called the US mainland a "boiled pumpkin" open to attack.
The North previously said it had put its strategic rockets on stand-by, threatening US military bases in Hawaii and Guam. But many analysts say the North does not have the capability to hit the US or realize many of its threats.
North Korea's leader Kim Jong Un has continuously responded with more than usual hostile rhetoric in recent months, after Pyongyang was slapped with new economic sanctions for its third successful underground nuclear bomb test.
At a meeting of the North Korea's ruling Workers Party Central Committee, Kim Jong Un denied Pyongyang was using its nuclear program as a negotiating tool.
"The nuclear weapons of Songun (military first) Korea are not goods for getting US dollars and they are ... (not) to be put on the table of negotiations aimed at forcing the (North) to disarm itself," KCNA news agency quoted him as saying.
Meanwhile, NBC News reported that the US Navy is moving a guided-missile destroyer – called the USS Fitzgerald – into the Pacific Ocean off the Korean Peninsula, citing US defense officials.
The move comes in spite of the fact that Washington said it saw little action to back up the North's threats.
"Despite the harsh rhetoric we're hearing from Pyongyang, we are not seeing changes to the North Korean military posture, such as large-scale mobilizations and positioning of forces," said White House spokesperson Jay Carney on Monday.
"We haven't seen action to back up the rhetoric."