SEOUL: North Korea fired several cruise missiles into the Yellow Sea on Saturday, Yonhap news agency reported citing the South Korean Joint Chiefs of Staff (JCS).

South Korean and US intelligence authorities were analysing the launches, which took place at about 4:00 am (local time), to learn more about the type of missiles fired and other details, according to the JCS.

"Our military has bolstered surveillance and vigilance while closely cooperating with the United States and maintaining a firm readiness posture," Yonhap news agency quoted JCS as saying.

The fresh launches have come just three days after North Korea fired two short-range ballistic missiles into the East Sea.

It also came amid heightened tensions on the Korean Peninsula following the port visit of a nuclear-capable US submarine in more than 40 years and the inaugural session of the South Korea-US Nuclear Consultative Group earlier this week.

USS Kentucky (SSBN 737), an 18,750-ton Ohio-class nuclear ballistic missile submarine (SSBN), departed Busan naval base on Friday, three days after a rare port visit in a major show of strength against evolving North Korean military threats.

North Korea denounced the visit, saying the SSBN's deployment may fall under the legal conditions for its use of nuclear weapons. This was met by a stern response from Seoul, which warned Pyongyang that any nuclear attack from the latter’s side would mean an “end” of the Kim Jong Un-led regime.