Asked if the North is the South's main enemy, Moon Jae-in of the liberal Democratic Party avoided a direct answer.

He said it's not an issue to be discussed in public by a "person seeking to become a (South Korean) president."

"It's work to be done by the Ministry of National Defense," Moon added.

Yoo Seong-min of the splinter conservative Bareun Party grilled Moon, claiming the "main enemy" wording is even included in the nation's defense white paper published by the Ministry of National Defense.

Moon, a former commando, has faced fierce criticism largely from conservatives who emphasize the reality of the two Koreas which remain technically at war as the 1950-53 Korean War ended in a truce.

They also highlight the North's repeated deadly attacks on the South including the 2010 sinking of the Cheonan warship in the West Sea and its continued development of nuclear and missile programs.

"If North Korea is not our main enemy, why I did I serve in the military?" read an Internet message. "Moon's comments prove he's not qualified to be president, namely the commander-in-chief of our military."

South Korea's 625,000 troops depend on the conscription of all able-bodied adult men under the Constitution.

Nonetheless, liberal-minded voters here say, efforts for peace talks with the North should go on, adding it's a potential dialogue partner in that sense and there's need to refrain from using words or acts that antagonize Pyongyang.

"In the 2016 white paper, the North Korean regime and military are described as our enemy," the ministry's spokesman Moon Sang-gyun said at a press briefing.

Another official confirmed that the words "main enemy" have not been used in the white paper since 2004.

"It's because (the expression) could cause various unnecessary misunderstandings," an official told reporters, apparently referring to an ideological rift among South Koreans over detailed ways of resolving the North Korea problem.

In its latest white paper issued in December, in fact, the ministry cited the North's development of weapons of mass destruction.

"As long as such threats continue, the North Korean regime and military, which are the source of the threats, are our enemy," it reads.

The official said it's the "strongest expression" for the ministry to use against North Korea without calling it the main enemy.

Meanwhile, South Korea's unification ministry said that North Korea is an enemy as well as a partner for peaceful unification, citing dual responsibilities of a South Korean president under the Constitution.

Article 66 of the Constitution stipulates that a South Korean president should defend the country as commander in chief while making efforts to bring forward peaceful unification.

"That's why South Korea sternly responds to North Korea's provocation while providing humanitarian assistance to the North if needed," said a ministry official, asking not be named. (Yonhap)