Seoul admitted Monday it was not clear how much of the wages paid to North Korean workers at a joint industrial zone were used to fund Pyongyang's nuclear and missile development.

The unification ministry said while the North's regime took 70 percent of the Kaesong workers' wages to fund state projects including arms development, it was unclear how much was funnelled into the nuclear and missile programmes.

Earlier Monday, unification minister Hong Yong-Pyo admitted there was no "clear evidence" what percentage of wages paid to the North Korean workers was used to fund Pyongyang's nuclear programme.

Hong had claimed Sunday about 70 percent of wages paid to North Korean workers at Kaesong were syphoned off to the North's ruling Workers' Party and used to develop nuclear weapon and missiles, or purchase luxury goods.

He used the claim to justify Seoul's decision last Wednesday to abruptly withdraw from the Kaesong industrial complex -- where South Korean firms operated factories that employed North Korean workers -- to punish Pyongyang for its latest nuclear and missile tests staged in violation of UN resolutions.

The shock pullout sharply escalated tension and imposed huge losses on the 124 South Korean firms operating at the industrial park.

Hong's comments Sunday sparked controversy over whether Seoul had been helping fund the North's widely-condemned weapons programmes.

However Hong, pressed by Seoul lawmakers to present clear evidence to back up his claim, said Monday he was simply "expressing concern" over such a possibility, according to Yonhap news agency.

"If there is clear proof for the North's misappropriation, it would constitute a breach of relevant UN resolutions," Yonhap quoted Hong as saying during a meeting with lawmakers.

"There are concerns about the North's misuse of the money, but I've not said that there is clear evidence," he said before apologising for "creating so much misunderstanding," according to Yonhap.

The zone, which sits 10 kilometres (six miles) north of the tense border, was officially shut last Thursday after Pyongyang expelled all South Korean managers and placed the complex under military control.

Since its opening in 2004, Seoul firms have paid wages worth $560 million -- including $120 million over last year alone -- to the North's state authorities supervising 53,000 workers at the complex.

Seoul was aware of the problem of wages being syphoned off but had maintained the project regardless due to its status as a symbol of inter-Korean cooperation, Hong said Sunday.

The isolated but nuclear-armed North staged its fourth atomic test last month and put a satellite into orbit on February 7 with a rocket launch that most of the wider international community condemned as a disguised ballistic missile test.