The arrest of two South Koreans on charges of attempting to hand over sensitive military equipment to North Korea has sparked fears about other possible hidden spies who pose a serious security threat.

The revelation on Wednesday is expected to add fuel to the ongoing controversy over leftist politicians in the Unified Progressive Party who were involved in pro-North Korea organizations in the past.

The two businessmen are accused of attempting to divulge advanced military technologies to the North, such as electronic jamming devices that could neutralize Seoul’s global positioning systems and a radar system for anti-aircraft defense, police said Wednesday.

“If North Korea secures such technologies, it would likely boost the accuracy of its intercontinental ballistic missiles and other rockets, interfere with the South Korean military’s operation of high-tech weaponry and thus undermine our deterrence against the North,” said Shin In-gyun, president of non-profit Korea Defense Network.

Authorities believe the suspects were behind the North’s recent jamming of aviation signals in the South. More than 650 commercial jets and 120 ships coming in and out of Seoul reported GPS disruptions for more than two weeks from April 28. Pyongyang denied responsibility.

The suspects had allegedly been following the instructions of a 40-something North Korean agent based in the Chinese city of Dandong near the North Korean border since July last year. Under his direction, they obtained military secrets via email from the former head of a domestic defense contractor, who was booked without detention.

One of them was convicted and sentenced to life in prison in 1972 for spying for the communist state. He was released on parole in 1990, though he refused to recant his political creed. The other is believed to be a 56-year-old New Zealand national and has been engaged in trade with North Korea since 2003.

The suspects were charged with violating the National Security Law and were transferred to the prosecution last week.

It was not immediately clear whether they handed over the equipment and other military intelligence to the North Korean agent.

Police also assume that a separate spy organization secured confidential data on location tracking technology used for ballistic missiles, based off clues from e-mails that Lee sent to Chung.

Authorities said they are looking into whether there are other covert groups working on North Korean missions. Technologies with a high potential for leaks also include Navy helicopters and radar-absorbing paint for stealth camouflage, they noted.

With Seoul’s heavy dependence on communications technology, concerns are mounting over its vulnerability to Pyongyang’s increasingly sophisticated military capabilities.

Controversy brewed in 2010 when a South Korean Army major general was indicted on charges of leaking classified military information to a North Korean agent. The two-star general passed part of the Operational Plan 5027, a war scenario jointly crafted by Seoul and Washington, in return for 26 million won ($22,000).

A North Korean state-run website on Wednesday proclaimed the North to be a nuclear-armed nation by publishing the text of its amended constitution. Its previous constitution, last revised in April 2010, did not articulate its nuclear status.

By Shin Hyon-hee (heeshin@heraldcorp.com)