Jay Lefkowitz had expressed concerns that North Korean workers in Kaesong industrial park are being exploited.

Officials at the South Korean Unification Ministry confirmed on Tuesday that Lefkowitz had been granted permission to visit the site - which is just on the northern side of the border.

Seoul had denied that workers in Kaesong are being treated poorly and urged the US to visit the site.

South Korean companies pay Northern workers at Kaesong about $50 a month - but the money is paid directly to the North Korean government and it has never disclosed how much the workers recieve.

In April, Lefkowitz said that workers were being mistreated and that there was no guarantee they were recieving their wages.

Seoul, which sees the project as an example of inter-Korean reconciliation, says that workers at Kaesong are paid more than in other parts of North Korea and that conditions there meet international labour standards.

Twelve South Korean companies operate in Kaesong, but South Korean officials hope that the low wages paid to Northern workers will draw 3,000 companies there by 2024.

The two Koreas remain technically at war, after the 1950-53 war ended only with a ceasefire agreement rather than a permanent peace deal.