Talks between North Korea and South Korea on how to lower tensions continued into the early hours of Monday, as Kim Jong Un stepped up the mobilisation of his forces.

Neither side showed any indication of when the meeting between Kim's top military aide Hwang Pyong So and South Korean President Park Geun Hye's chief security adviser Kim Kwan Jin, which began at 3:30 p.m. on Sunday, might end. It follows a 10-hour session between the officials earlier in the weekend.

As the dialogue went on at the border village of Panmunjom, a South Korean military official said North Korea had dispatched more than two thirds of its submarines from ports and doubled its front-line artillery forces.

A South Korean soldier carries a barricade at a checkpoint on the Grand Unification Bridge which leads to the truce village Panmunjom, just south of the demilitarised zone separating the two Koreas, in Paju, South Korea. Reuters

The standoff, with both countries' forces on a high alert for any possible military clashes, is one of the most serious since Kim became Supreme Leader in late 2011. An uneasy truce on the peninsula is periodically disrupted by exchanges of rockets or gunfire that peter out before they escalate, though the unpredictable regime in Pyongyang keeps tensions high.

Tensions have escalated in recent weeks across the DMZ that bisects the peninsula more than 60 years after the Korean War. Two South Korean soldiers were injured Aug. 4 by land mines that the government in Seoul said were recently laid by North Korea. North Korea denied setting the devices.