SEOUL - North Korea carried out a live-fire drill near the disputed sea border with South Korea Thursday for the second consecutive day, snubbing calls from Seoul not to escalate cross-border tensions.
The drill began at 7:10 pm (1010 GMT) near a South Korean front-line island close to the maritime border in the Yellow Sea, the South's Defence Ministry said.
"South Korean troops are keeping a tight guard against any provocations from North Korea," a ministry spokesman told AFP.
South Korea has vowed to react "sternly" if North Korean shells fell south of the border.
South Korea accused North Korea of firing about 130 shells from a war ship and its coast artillery for 85 minutes from 9:00 pm on Wednesday near the sea border.
No artillery rounds fired by North Korea late Wednesday landed on the south side of the border, but Seoul urged Pyongyang to stop its "threatening act".
The North's military has said it would stage the firing drills between Wednesday and midnight Friday in its territorial waters.
Cross-border tensions have soared since Pyongyang's state media announced Saturday that a new submarine-launched ballistic missile (SLBM) had been successfully tested under the personal supervision of North Korean leader Kim Jong-Un, who described it as a "world-level strategic weapon".
The North followed up the SLBM launch by test firing three anti-ship cruise missiles on Saturday.
Pyongyang has also threatened to fire on sight at South Korean navy patrol boats it accuses of routinely entering its territorial waters in the Yellow Sea.
Seoul has denied any incursions.
The two Koreas recognise different boundaries dividing their territorial waters in the Yellow Sea.
The maritime border has always been a flashpoint and was the scene of brief but bloody naval clashes in 1999, 2002 and 2009.
In November 2010, North Korea shelled Yeonpyeong island, killing four South Koreans and briefly triggering concerns of a full-scale conflict.
Most recently, North and South Korean naval patrol boats briefly exchanged warning shots in October last year.
Because the Korean conflict ended with a ceasefire rather than a treaty, the two Koreas remain technically at war.