South Korea says North hacked phones of key officials

South Korea's spy agency says North Korea had hacked into smartphones belonging to a number of key government officials, part of a series of cyber-attacks launched after its fourth nuclear test.

File North Korean news agency KCNA image showing Kim Jong Un meeting millitary personnel during rocket test-firing. Source: AAP

The revelations by the National Intelligence Service (NIS) came as the government is seeking to push through parliament an anti-cyber terrorism law that critics say would grant the agency unmatched surveillance powers over cyberspace, including messenger servicing networks.

In a statement, the NIS said the North stole phone numbers and texts from the smartphones of dozens of key South Korean officials between late February and early March.

It also attacked the server of a major software firm specialising in providing security software for Internet banking.

"North Korea has been mounting a series of attacks against our cyberspace" following its nuclear test on January 6, the statement said, adding that they appeared to have been preparation for a major cyber assault on South Korea's banking network.

"If left unchecked, it would have resulted in major financial chaos, such as paralysis of Internet banking systems and unwanted transfers of deposits", it said.

According to the agency, North Korean hackers also sent text messages to the South Korean officials, trying to lure them to links infected with malware that could capture the phone numbers of other officials.

Presiding over a meeting Tuesday with 14 government agencies, as well as the defence ministry, Financial Services Commission and science ministry, an NIS deputy director urged them to maintain a high level of vigilance.

Seoul has blamed North Korean hackers for a series of past cyber-attacks on military institutions, banks, government agencies, TV broadcasters and media websites as well as a nuclear power plant.

The United States also said the North was behind a damaging cyber-attack on Sony's Hollywood film unit over its controversial North Korea-themed satirical film "The Interview" in 2014.

A spokesman for the presidential Blue House said the growing cyber threat from the North added urgency to the passage of the anti-cyber terror law, now pending in the National Assembly.

But the main opposition Minjoo Party said the government was exaggerating the threat to secure surveillance powers for the NIS that could be used against political opponents.

A former head of the NIS was jailed for three years in February 2015 for meddling in the 2012 presidential election.