SEOUL, South Korea (AP) _ A Defense Ministry official said South Korean naval vessels backed by jet fighters sank a North Korean spy boat Sunday after it opened fire when caught trying to sneak to shore near the southern port of Pusan.

There was no immediate comment from North Korea's communist authorities on the reported gun battle.

Gen. Chung Jin-kwon, chairman of South Korea's Joint Chiefs of Staff and head of the Counter-Espionage Command, said the armed boat was sunk 18 miles southeast of Chongsa-po, a fishing port 12 miles north of Pusan, about three hours after it was spotted.

Chung said there were no casualties on the South Korean side, but did not say whether any bodies were recovered from the sunken boat.

He said coast guard units spotted the boat trying to sneak to shore and called in the navy for help.

Chung said the boat defied signals to halt and opened fire, causing slight damage to South Korean vessels. When the boat tried to flee, Chung said the naval ships, assisted by air force planes, sank it.

He said debris recovered from the boat included diving suits, a map and other equipment he said could be used for infiltration.

The Yonhap News Agency in South Korea quoted unidentified sources as saying the North Korean boat was 28 feet long and 8 feet wide and could carry a crew of six.

Chung said authorities believed the alleged infiltration was an attempt to instigate social unrest in industrial and other facilities in Pusan, South Korea's second-largest city.

It was the first time South Korea had claimed to have crushed a North Korean infiltration attempt along the southern coast since South Korea sank a North Korean spy boat and captured two armed agents in December 1983.

Chung urged vigilance against possible armed provocations by North Korea. He accused the North of attempting to send in armed agents while the two Koreas were engaged in dialogue.

The two sides, which fought a bloody war in 1950-53, have been discussing economic cooperation, the reunion of families separated by the Korean peninsula's division and other issues.