During a meeting with the supporters, Moon called conservatives' much-flaunted security policy capability "bogus" and accused them of seeking to make use of security issues for electoral gains.

"I will sternly confront bogus security forces that consider security their (political) tool without any proper views about the nation and security," Moon said during the meeting at the National Assembly.

"The Democratic Party and I will pursue genuine security, not fake security," he added.

National security has been cited as one of his weaknesses as he has called for delaying the installation of a US missile defense system on the peninsula to allow the next government to make a decision on the key security issue.

Concerns about his stance on security further escalated as he refused to publicly brand Pyongyang a "main enemy" on the grounds that the labeling would hamper diplomacy toward the North to establish peace on the peninsula and achieve reunification.

Further fueling the concerns is a former foreign minister's renewed claim that when Moon was a chief presidential aide in 2007, Seoul decided to abstain from voting on a UN resolution against the North's human rights violations after consulting Pyongyang.

To dispel such worries, Moon has vowed to focus on bolstering national defense.

"Defense and security are more important than any other time as the North's nuclear and missile threats are becoming tangible," Moon said during the meeting.

"Despite the international community's sanctions and pressure, the North is obsessed with advancing its nuclear and missile capabilities, and threatening security on the Korean Peninsula," he added.

Later in the day, Moon visited an Army training center in Pocheon, 46 kilometers north of Seoul, to observe a large-scale artillery exercise. 

There, he stressed the need for the military to make "all-out" efforts to ensure national security, while pointing to Pyongyang's recent saber-rattling, including its display of various weapons during a military parade earlier this month.

"Today's exercise has the effect of showing off our capabilities to strongly and immediately retaliate if provoked and allaying citizens' (security) concerns," Moon said.

"I observed the exercise, thinking that presidential candidates must pay due attention to (security) based on the belief that both ruling and opposition parties should be united in efforts to ensure a readiness posture," he added.

Moon has long maintained a lead over all other contenders in voter surveys, trailed by Ahn Cheol-soo of the center-left People's Party. All conservative candidates remain in woeful single digits amid speculation that they could seek some political alliance to thwart Moon's campaign. (Yonhap)