South Korea and the United States kicked off a combined naval exercise in the East Sea on Monday to reinforce readiness against growing military threats from North Korea, the Navy said.

The three-day exercise involved nine vessels and two patrol aircraft from the two sides, including two South Korean submarines, the ROKS Yulgok Yi I destroyer, the USS Shoup Aegis-equipped destroyer and the USS Robert Smalls cruiser, the Navy said.

The Navy said the anti-submarine warfare and live-fire drills were designed to strengthen the allies' combined operational capabilities and interoperability amid evolving nuclear and missile threats from the North, including its recent claimed launch of a space launch vehicle and unveiling of a new submarine.

"This exercise will serve as an opportunity to effectively deter and respond to North Korea's nuclear and missile threats and further solidify the combined defense posture," R. Adm. Kim In-ho, who led the South Korean side during the exercise, was quoted as saying.

The North has continued to ratchet up tensions on the Korean Peninsula, vowing to launch a military spy satellite next month after two failed attempts in May and August, respectively. It also held a launching ceremony for a new "tactical nuclear attack" submarine earlier this month. (Yonhap)