North and South Korea dug in their heels Friday in an escalating row over wages at their Kaesong joint industrial zone.
Pyongyang last month announced it would raise the basic salary of some 54,000 North Korean workers employed across 125 South Korean firms in the complex.
But the South rejected the idea, citing an existing agreement that any wage rise had to be agreed by a joint committee overseeing the management of the park, which lies just over the border in North Korea.
"The government can never accept any unilateral system change," South Korean Unification Ministry Spokesman Lim Byeong-Cheol told reporters Friday.
Voicing "regret" at Pyongyang's refusal to engage with Seoul's offer of a dialogue on the issue, Lim said the ministry would work closely with company managers in Kaesong to resolve the dispute.
The North's proposal would increase the average monthly sum the South pays for each worker -- including allowances, welfare and overtime -- from $155 to $164.
On Thursday, North Korea said it had no need to consult with the South over the wage hike, saying it had a "legitimate and normal" right to amend working conditions in Kaesong.
"There is absolutely no reason for us to review our rights ... with the South concerning Kaesong where our sovereignty reigns," said a spokesman for the Central Special Development Guidance Bureau, which is in charge of operations at the complex.
In an interview with the North's state-sponsored news website Uriminzokkiri, the spokesman argued that the skills of the workers in Kaesong had improved markedly since the zone was set up in 2004, and deserved greater remuneration.
A rare symbol of cross-border cooperation, Kaesong had previously been spared the fallout from the regular eruptions in relations between the two Koreas.
But the North effectively closed down the park for five months in 2013 following a surge in military tensions.
When it reopened in September that year, the two sides created the joint committee to deal with any further problems related to its operations.