North Korea's immediate threat to South Korea has grown, with 20,000 more special warfare troops deployed near their border along with 200 new tanks, a defense white paper published by the South on Thursday said.
The publication of the biennial report comes as tensions on the divided peninsula are at their highest in decades following North Korea's shelling of a South Korean island in November.
The size of the North's military remained steady from two years ago at 1.19 million troops, the defense ministry paper said, but its "asymmetrical threat" grew with Pyongyang's continued pursuit of weapons of mass destruction.
South Korea has reinstated its "enemy" designation for the North after having dropped it in 2000, when the two Koreas held the first of only two summit meetings between their leaders that led to warmer ties and the start of commercial exchange.
The heightened tension has worried regional powers, with China, the North's main ally, on Thursday repeating its call for dialogue and Russian Deputy Foreign Minister Alexei Borodavkin calling on the two Koreas to stop "muscle flexing."
The sinking of a South Korean warship in March that Seoul and its ally the United States blamed on a North Korean submarine attack, and last month's artillery barrage, had led the South to raise its guard, the defense ministry said.
The attacks led to exchanges of threats between the rival Koreas, with some analysts saying the chance of a wider conflict was greater than ever.
"In view of recent security conditions, we specified the North's regime and its military as our enemy," South Korean Defense Ministry policy planning chief Chang Kwang-il said.
Chang said the North's special forces numbered 200,000 troops and it continued to strengthen tactical warfare capabilities along the heavily armed border, with new units being added.
The North is believed to have 200 more tanks than previously identified, at 4,100 units, but the scale of its artillery firepower remained roughly equal to two years ago, the white paper said.
North Korea bombarded an island near the disputed maritime border off the peninsula's west coast in late November with 170 rounds of artillery in what it said was a defensive move against an imminent South Korean attack.
The shelling killed four people and drew a vow by the South to retaliate forcefully if there was any repeat.
North Korea channels much of its scarce resources into building a military under its homegrown "military first" policy that mixes Marxism with nationalism.
North Korea has deployed mid-range missiles that can hit all of South Korea and Japan and threaten U.S. military bases in Guam. The North already has hundreds of ballistic missiles that can hit most parts of the South.
The white paper kept its earlier estimate of the North's plutonium stockpile at 40kg (88lb), which experts believe would be enough for at least five nuclear weapons.
Experts do not believe the North, which has twice conducted nuclear tests, has the technology to make an atomic weapon small enough to mount on a functioning delivery system.