Seoul: North Korea`s military Tuesday threatened "strong physical retaliation" against a South Korean naval exercise set to start this week in the Yellow Sea.
The South is staging the anti-submarine drill from August 5-9, involving the Army, Navy, Air Force and marines, in response to what it says was a deadly North Korean torpedo attack on a warship.
It follows a major US-South Korean naval and air exercise held last week in the Sea of Japan (East Sea) as a warning to the North.
Pyongyang threatened nuclear retaliation for last week`s drill but it passed without incident.
The military`s western command, in a notice quoted by the official news agency Tuesday, described this week`s South Korean exercise as a "direct military invasion".
"In view of the prevailing situation, the (western command) made a decisive resolution to counter the reckless naval firing projected by the group of traitors with strong physical retaliation," it said in a reference to South Korea.
The disputed maritime border in the Yellow Sea has been the scene of several naval clashes. In March, a South Korean corvette sank in the area with the loss of 46 lives.
South Korea, the United States and other countries, citing findings of a multinational investigation, said a North Korean submarine had fired a heavy torpedo in an attack which broke the warship in two.
The North vehemently denies responsibility, calling the allegations a "smear campaign" to provide a pretext for aggression.
It refuses to recognise the sea border drawn by United Nations forces after the 1950-53 war, insisting it should run further to the south, and repeated this stance Tuesday.
The North`s military warned civilian ships including fishing boats not to enter the area of naval firing fixed by the South, which it said would be close to five islands near the border.
"It is the unshakable will and steadfast resolution of the army and people of the DPRK to return fire for fire," it said.
The South`s Joint Chief of Staff said marines stationed on islands near the border would stage live-fire exercises but naval ships would stay far south of the line.
The North routinely denounces joint military exercises south of the border as a rehearsal for war, while the United States and South Korea say they are purely defensive.
Some 28,500 US troops are based in the South.