North Korea has boosted its "cyber army" in a bid to cause "physical and psychological paralysis" in the South.

According to the South Korean Defence Ministry's latest white paper, the hermit state's military unit, which is dedicated to cyber activities, is now double that of South Korea's.

"North Korea is currently running its 6,000 (member) workforce for cyber warfare and performing cyberattacks for physical and psychological paralysis inside South Korea such as causing troubles for military operations and national infrastructures," said the South Korean Defence Ministry.

In 2013, South Korea blamed Pyongyang for the raft of crippling cyber attacks on its banks and broadcasters.

North Korea has been blamed by the US for the large scale hacking of Sony Pictures after it initially refused to pull the screening of a movie involving the death of the hermit state's leader.

The Interview stars Seth Rogen and James Franco as a television personality and his producer, who manage to net an interview with Kim Jong-un. They are then approached by the CIA, who instruct them to kill him.

Hackers had demanded the movie not be screened.

Sony Pictures was then hit by a vast cyber security breach which has led to unidentified hackers leaking unreleased movies, emails between senior executives, and confidential information relating to members of staff.

This includes social security numbers, salaries, healthcare records, performance evaluations and reasons for termination.

Furthermore, Sony Pictures is also being sued by two former employees for failing to protect key staff pay and conditions data from hackers.

While Pyongyang has denied involvement in the attack, South Korea has grown closer as an ally to the US over the event.

At the beginning of this year, US President Barack Obama authorised new sanctions on North Korea in response to the cyberattack on Sony Pictures.

In a statement from the White House, the sanctions were described as the "first aspect of our response" to the hack.

According to the Washington Post, the sanctions are aimed at arms companies. The sanctions affect three North Korean companies and ten North Korean government officials, including individuals working in Iran, Syria, China, Russia and Namibia, the Obama administration said.

President Obama said he ordered the sanctions because of "the provocative, destabilising, and repressive actions and policies of the Government of North Korea, including its destructive, coercive cyber-related actions during November and December 2014.

"The order is not targeted at the people of North Korea, but rather is aimed at the Government of North Korea and its activities that threaten the United States and others," Obama added.