Report: Two Koreas' navies in skirmish

STORY HIGHLIGHTS
* North and South Korean naval forces exchange fire, Yonhap news agency reports
* Clash happened off their west coast, where previous skirmishes turned deadly
* N. Korean patrol ship entered S. Korean waters, prompting South to fire warning shots
* North Koreans then fired back, an unnamed South Korean defense official said

(CNN) -- North and South Korean naval forces have exchanged fire, South Korea's semi-official Yonhap news agency reported Tuesday.

The two Koreas clashed off their west coast, where previous skirmishes in 1999 and 2002 turned deadly, Yonhap reported, citing an unnamed South Korean defense official.

"No South Korean casualties were immediately reported," the official said.

He said a North Korean patrol ship crossed into South Korean waters, prompting the South's navy to fire warning shots, according to Yonhap.

"The North Koreans then fired back," the official said.

The two Koreas dispute the exact location of the sea border between their countries.

A clash in 2002 followed a series of incursions by navy ships from North Korea into South Korean waters. At least four South Korean sailors died in that incident and nine others were wounded.

In June 1999, several border violations by North Korean ships sparked the first naval clash between the two Koreas since the 1950-53 Korean War.