Governments around the world have condemned North Korea for conducting its third nuclear test since 2006. Pyongyang confirmed the test hours after seismic sensors registered a possible underground explosion.
South Korea has demanded the release of two of its citizens being held by the North on allegations of spying. Seoul has also denied that the two men were involved in espionage operations against the North.
South Korea has vowed to bolster cyber security after hackers allegedly targeted nuclear plants. Seoul claimed that intention of the breaches was to cause a malfunction and promote civil unrest, endangering lives.
US President Barack Obama has issued an executive order which will allow economic sanctions on US and foreign hackers. The move will enable authorities to punish individuals, as well as entities engaged in cyber attacks.
North Korea tested missiles and warned it will carry out "merciless strikes" against the US and South Korea. The allies are launching joint military drills.