The North is currently facing a concerted diplomatic push by world powers.
It will host the UN's top political envoy later this week, with analysts saying this engagement may bode well for the dormant six-way disarmament-for-aid talks and could lead to Pyongyang reducing the security threat it poses to the region.
Separately, South Korea sent a team across the border for talks in the border city of Kaesong on joint tourism projects in the North run by an affiliate of the South's Hyundai group.
The tours, suspended for more than a year, once earned the North's leaders tens of millions of dollars a year.
A few hours after discussions began North Korea's official media ran a report where it quoted state security officials as saying the country was ready to strike those in the South who were plotting to overthrow Pyongyang's leaders.
Citing a statement from two North Korean security ministries the report said Pyongyang has a secret strike force to counter what it called Seoul's plots.
"We have world-level ultra-modern striking force and means for protecting security which have neither yet been mentioned nor opened to the public in total," the report said.
The North, which often alleges such plots, cited the South's demands that Pyongyang undertakes to scrap nuclear weapons before any broader settlement of differences.
The North's security ministries also criticised efforts by the South's military
to defend the disputed Yellow Sea border – where the North fired artillery late last month – and "reckless" operations to destabilise the North.