Pyongyang also said it was shutting down two crucial cross-border communications hotlines.
State media reported that tens of thousands of North Korean employees would also be pulled out, with South Korean assets frozen and cross-border communications shut down.
It also said it was restoring cross-border communications lines it had cut off earlier this year out of anger over joint United States-South Korean military drills.
The International Telegraphic Union was founded in 1865 to facilitate speedy cross-border communications, and the Universal Postal Union followed in 1874.
"Cross-border communications have been improved, command levels at border coordination centers have increased, and command relationships have been redefined where needed," Lt. Col. Jimmie E. Cummings Jr., a NATO spokesman, wrote by e-mail.
There has been no public disclosure of any ruling by the Foreign Intelligence Surveillance Court explaining its legal analysis of the 2008 FISA law and the Fourth Amendment as allowing "about the target" searches of Americans' cross-border communications.
That prompted the North to open a cross-border communications hot line on Wednesday and invite South Korean factory owners and engineers to return to Kaesong to do maintenance work on their equipment before the possible reopening of the complex.
But in a world where most governments have long since lost their monopoly over cross-border communications, top-down structures are not suitable forums for making difficult decisions about Internet policy.
The counteroffer was delivered to North Korea through a Red Cross hot line, the first restored among several cross-border communications lines North Korea had unilaterally cut off recently in anger over joint South Korean-American military exercises in March.
SEOUL, South Korea — North Korea and South Korea plan to open modernized military telephone lines next week to improve cross-border communications, the South Korean Defense Ministry said Tuesday.
TeleGeography analyst Stephan Beckert refers to Skype's estimated volume of traffic as "tremendous" and goes on to say that Skype is now by far the largest provider of cross-border communications in the world.
