North Korea on Thursday threatened more military attacks in response to any South Korean "provocation" and said the United States is partly to blame for a deadly artillery barrage this week.
"If the warmongering South Korean puppets fail to return to their senses and commit another reckless military provocation, our army will carry out second and third rounds of powerful physical retaliatory strikes without hesitation," a representative of the North's military said.
North Korean artillery batteries pounded a South Korean border island on Tuesday, killing four people and sparking global alarm.
The North says the South's military was to blame because it fired into the North's maritime territory during an exercise, a charge denied by Seoul.
Washington is also at fault for its role in drawing the "illegal" sea border in the aftermath of the 1950-53 Korean War, the representative said in a message to the US military quoted by the official news agency.
"The West Sea of Korea (Yellow Sea) has become a flashpoint where the risk of confontation and clashes between the North and the South is persistent just because the US unilaterally drew the illegal Northern Limit Line," he said.
"Therefore, the US can never evade responsibility for the recent exchange of fire."
The agency said the North's military representative at the border truce village of Panmumjom was responding to US charges that the North's attack breached the armistice in force since the war.
The North refuses to recognise the Northern Limit Line drawn unilaterally by US-led United Nations forces at the end of the war. It demands it be redrawn further south.
The disputed border was the scene of deadly naval clashes in 1999, 2002 and last November.