A South Korean naval patrol ship (L) approaches its floating base before the sun rises off Yeonpyeong Island November 28, 2010. [Photo/Agencies]

SEOUL - Republic of Korea (ROK) and the United States on Sunday launched a four-day joint naval drill in tense waters west of the divided Korean Peninsula.

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The drill, conducted five days after the artillery skirmish between Republic of Korea (ROK) and the Democratic People's Republic of Korea (DPRK) off the west coast, is centering on antiaircraft defense and naval surface warfare.

Calling the drill "defensive in nature", the US Forces Korea (USFK) here said in a statement it "demonstrates the strength" of the alliance between Seoul and Washington and their "commitment to regional stability through deterrence." It is also designed to improve the two nation's military interoperability, it said.

According to reports, the USS George Washington, a nuclear- powered 97,000-ton carrier is taking part in the drill, along with the USS Cowpens cruiser, the USS Stethem destroyer, the USS Fitzgerald and the USS Shiloh.

The South Korean military sent two destroyers, a naval patrol ship and an antisubmarine warfare aircraft to take part in the exercise.

China has expressed its opposition to any military operations in its exclusive economic zone without permission.

"We hold a consistent and clear-cut stance on the issue. We oppose any party to take any military actions in our exclusive economic zone without permission," China's Foreign Ministry spokesman Hong Lei said in a statement days before the ROK- US joint drill.  

Tensions are high on the Korean Peninsula after the two sides exchanged fire last Tuesday in waters near the contentious sea border called the Northern Limit Line (NLL). The artillery clash left four South Koreans dead, while damage to the DPRK still remains unknown.

South Korea and the DPRK have remained at odds on the so-called NLL, which was fixed unilaterally by the US-led United Nations Command after the 1950-1953 Korean War. ROK holds the NLL as the de-facto western inter-Korean border, but the DPRK rejected the NLL and only recognized the demarcation line it drew in 1999, which was further south of the NLL.