South Korea on Tuesday accused North Korea of hacking the smartphones of government officials, and unveiled new sanctions on Pyongyang over its recent nuclear test and long-range rocket launch.

The National Intelligence Service (NIS) -- the South's spy agency -- said the North had stolen phone numbers and texts from the phones of dozens of key officials between late February and early March.

North Korean hackers also sent phishing emails to employees of two provincial railway operators in an attempt to steal passwords that could have allowed a cyber-attack on rail traffic control systems, the agency said in a statement.

"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.

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.

The NIS revelations came as Seoul unveiled a series of fresh unilateral sanctions against Pyongyang and asked citizens to boycott North Korean restaurants abroad.

The new measures blacklisted scores of North Korean individuals and entities and banned any vessels previously docked in North Korean ports from South Korean waters.

They follow tough sanctions adopted by the UN Security Council last week and -- though largely symbolic given the lack of North-South economic ties -- are likely to prompt an angry response from Pyongyang.

"Since North Korean facilities such as overseas restaurants are one of North Korea's channels for foreign currency, we ask the public to refrain from using these facilities," said Lee Suk-Joon, head of the Office for Government Policy Coordination.

The South Korean government estimates that Pyongyang rakes in around $10 million every year from some 130 restaurants in 12 countries.

Lee said the government suspected most of the foreign currency was "ultimately being used for weapons of mass destruction."

The move to ban foreign vessels that have previously docked in the North would appear to spell the end of an ambitious trilateral infrastructure project aimed at transporting Russian coal to South Korean ports through the North's port city of Rajin and Russia's border town of Khasan.

The so-called Rajin-Khasan project was viewed as an integral part of South Korean President Park Geun-Hye's vision of uniting the railways of South and North Korea to connect them to Europe.

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