SEOUL, South Korea (AP) -North Korea banned boats off its west coast, a South Korean official said Friday, in a possible indication the country may hold an artillery drill or even conduct missile tests.
The official with the Joint Chiefs of Staff said that South Korea is closely monitoring the North's military, though he added that no unusual movements had been detected.
He declined to give further details and asked not to be named as the matter involves military intelligence.
South Korea's Yonhap news agency cited an unidentified government source as saying the no-sail zone was set from June 19-27 north of the port of Nampo, 50 miles (80 kilometers) from the disputed inter-Korean sea border.
The North has set similar restrictions before past missile tests or firing drills. In January, North Korea designated no-sail zones and fired artillery as part of an annual drill near the western sea border.
The poorly marked sea frontier - drawn by the American-led U.N. Command at the end of the 1950-53 Korean War - is a constant source of tension between the divided Koreas. Their navies engaged in bloody battles in the area in 1999, 2002 and last November.
The North's latest move came amid heightened tensions over the deadly sinking of a South Korean warship near the western sea border in March that killed 46 South Korean sailors.
A multinational investigation led by South Korea concluded in May that North Korea torpedoed the 1,200-ton vessel. South Korea has since asked the U.N. Security Council to punish Pyongyang over the sinking.
The North, however, has flatly denied responsibility and threatened to respond to South Korean retaliatory measures with war.
South Korean President Lee Myung-bak urged Pyongyang to own up to the sinking on Friday as Seoul marked the 60th anniversary of the outbreak of the Korean War, which ended in a cease-fire, not a peace treaty.
"North Korea should clearly and frankly admit and apologize for its wrongdoing over its provocation," Lee said in a speech. He also called on Pyongyang to assume a responsible attitude in the international community and "stop reckless military provocations."