North Korea, one of the world's most-sanctioned states with few items it can legitimately export, has been sending its workers to places including Russia and the Middle East for decades to help bolster its coffers.
It now appears to be sending them to more places including Africa, said the official who asked not to be named.
"We believe North Korean construction workers have been employed in South Africa, including at World Cup stadiums," the South Korean official said.
South Korean media said as many as 1,000 North Korean workers have been working to build or upgrade the stadiums in Johannesburg and Nelspruit.
North Korea's already wobbly economy has been hit by fresh U.N. sanctions imposed after its nuclear test last May that cut into what had been a lucrative source of income through illicit arms sales.
The North's economic woes, made worse by a botched currency move late last year, have put pressure on it to return to stalled nuclear disarmament talks where it can win aid for decreasing the security threat it poses to the region.
South Africa, hosting Africa's first World Cup in June, has invested billions in infrastructure for the games.
North Korea will be competing in the World Cup Finals for the first time since 1996 where they face Brazil, Ivory Coast and Portugal in Group G.
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