South Korea unveiled two cases of North Korean spies in less than a week, fraying the nerves of opposition politicians who prioritized reconciliation with Pyongyang or even once worked for pro-communist organizations.

The National Intelligence Service said Friday that it is investigating a female North Korean defector on suspicion of spying for her homeland.

Lee Kyung-ae, 46, who entered Seoul via Thailand late last year, reportedly confessed that she was an undercover agent for the North’s military intelligence unit.

According to reports, she was professionally trained as a spy in the early 2000s. She was dispatched to China and dealt with counterfeit bills worth up to $1 million.

She also assisted the North’s investigation of a Korean-American man, born in the North, suspected of working for the U.S. Central Intelligence Agency.

“It is true that she is under investigation,” an official at the NIS said.

The NIS began the investigation because of her dubious explanation of her life in China and North Korea. When entering South Korea, she had told the authorities that she had lived together with a South Korean man in China. She said after the mate left for the South, she decided to follow him.

The NIS and the prosecution are investigating her purpose of entry and her activities in the South.

The revelation came two days after police arrested two South Korean businessmen on charges of attempting to divulge sensitive military technologies to the autocratic regime.

They are suspected of trying to pass electronic jamming gears and a radar system for anti-aircraft defense.

The disclosures came at a sensitive time when leftist politicians of the United Progressive Party are criticized anew for their past pro-North Korea activities.

Both conservative and liberal parties are demanding Lee Seog-gi and Kim Jae-yeon resign. They were members of activist groups following the North’s state philosophy of “juche.”

The UPP’s leftists have refused to clarify their stance on the North’s hereditary power handover, communist principles and human rights issues, triggering worries that their membership of the fledgling National Assembly could risk national security.

The spy cases are also expected to deal a blow to the main opposition Democratic United Party, which had advocated closer ties with Pyongyang when its members were in power between 1998-2008.

One of the businessmen accused of smuggling of military secrets was convicted and sentenced to life in prison in 1972 for spying for the communist state.

The liberal government in 1990 released him on parole, though he refused to relinquish his political creed.

Critics take issue with potential political motivations behind the revelation of the investigations, which come at a heightened period of ideological tensions in a crucial election year.

While acknowledging underlying security risks, critics label them as an attempt to inflame popular sentiment and sway the December presidential vote.

Civic groups have claimed that the National Security Law has often been used by those in power as an instrument of oppression against democracy, peace, labor and human rights movements here.

Cross-border tensions have been rising since the nuclear-armed state’s a botched rocket launch in April. Conservative lawmakers, government officials and even President Lee Myung-bak relayed criticism against pro-North figures.

“What North Korea claims is a problem, pro-North Korean forces among us echo that it is even a bigger problem,” Lee said Monday on a biweekly radio address.

Such tactics have often held sway in past elections. Nearly all presidential elections in democratic Korean history have seen similar communist labeling attempts, either by the incumbent government or challengers, just a few months before voting began.

“It is pathetic and ridiculous that the president would bring up such outdated politics of prompting an ideological strife. Such a witch hunt doesn’t help the party innovate itself and get back on its feet,” the UPP’s interim leader Kang Ki-kab said.

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