South Korea's defence chief on Friday pledged strong revenge for any provocations by North Korea in an order marking the anniversary of a cross-border gunfight a year ago.
"We need thorough punishment against provocations by the enemy," Defence Minister Kim Kwan-Jin said in his order.
The attack killed two South Korean Marines and two civilians and damaged scores of buildings.
"Our military has been burning with rage," Kim said, adding South Korean soldiers should "bear the responsibility to beat the enemy and pay them back at any cost".
The North has reinforced its coastal artillery with dozens of new cannons aimed at Yeonpyeong, the South's Yonhap news agency said Friday.
The extra deployment of 76.2mm guns with a range of 12 kilometres (7.2 miles) came after the South sent extra weaponry to five islands near the disputed sea border, it said.
The defence ministry declined to comment. Yeonpyeong is only 13 kilometres from the North's artillery.
"It's seen as a reaction to the reinforcement of our weaponry on (frontline) islands," an unnamed military official told Yonhap.
Relations have been tense since Seoul accused its neighbour of torpedoing a South Korean warship in March 2010 near the Yellow Sea border, with the loss of 46 lives.
The North denied sinking the ship, but South Korea has since staged a series of military drills alone or jointly with US troops.
In a commentary on Friday, the North's ruling party newspaper Rodong Sinmun said tension was rising near the sea border because of "provocative" live-fire drills and other exercises by South Korean troops.
It also accused the South of creating "a dangerous situation" in the Yellow Sea.
"Military tension around five islands off the west coast is getting acute day by day," the commentary said.