SEOUL-- South Korea's spy agency on Thursday raised the possibility of additional North Korean nuclear and missile tests, saying Pyongyang would continuously push to develop "miniaturized, diversified" warheads.

During a parliamentary audit, the National Intelligence Service (NIS) also said that Pyongyang could likely begin the work of reprocessing spent fuel rods at its main nuclear complex in Yongbyon late this year.

"The North will carry out additional nuclear tests and continue to push for the development of miniaturized, diversified nuclear warheads," the NIS was quoted by lawmakers who attended the audit as saying.

The NIS said that there has been "active movement" of vehicles around the missile research facility in Pyongyang -- an indication that the reclusive regime could resume its provocations for the first time since the latest one in September.

The agency also said that Tunnel 3 at the Punggye-ri test site is ready for a nuclear test "at any time," while it would take a considerable amount of time to prepare Tunnel 4 for a new underground nuclear experiment.

The NIS, in addition, noted the possibility of damage at the nuclear test site, pointing to three aftershocks that occurred following the North's sixth and most powerful nuclear test on Sept. 3.

The NIS also said it had detected signs of Pyongyang having attempted to hack into South Korea's financial institutions.

Amid international restrictions on its efforts to gain foreign currency, the hacking group under the Reconnaissance General Bureau, the North's core military spy agency, appears to be using online attacks for financial gain, the NIS said.

"We have detected circumstantial evidence that the North has persistently been trying to glean information needed for targeting and hacking into multiple financial institutions such as the virtual currency trading agency, banks and securities firms," the agency said.

"We anticipate that the North's hacking may focus on (extorting) virtual money that is hard to keep track of and may seek the destruction of the financial system, which could cause social confusion," it added.

On the terrorism issue, the NIS said that since 2010, a total of 71 foreigners from nine countries have been deported for their alleged links to terrorist organizations.

"International terrorist organizations such as the Islamic State (IS) have threatened terrorist attacks on our country 13 times since 2004," the agency added.

The NIS enumerated three threat factors ahead of the 2018 PyeongChang Winter Olympics: global terrorist networks such as the IS militant group, homegrown "lone wolf" attacks and the constant threats from the belligerent North.

Explaining North Korean leader Kim Jong-un's governing style, the NIS said that he has apparently resumed a campaign to purge dissenters or those seen as disloyal to him.

"Chairman Kim has recently strengthened the monitoring of his senior officials and resumed the purge and executions that he had refrained from for some time," the agency said.

The NIS also said that it would wrap up its probe into its alleged misdeeds during past governments this month, and that it would seek to craft measures to prevent them.

The agency has been carrying out an extensive internal investigation into allegations of its political interference and other wrongdoings as part of its broader reform scheme.

Source: Yonhap News Agency