North Korea’s decision to cut off military communications with South Korea is now preventing South Koreans from visiting an inter-Korean industrial complex in the North Korean city of Gaeseong.

Pyongyang announced that it would shut down the last remaining inter-Korean communication channel for the duration of the 12-day South Korea-U.S. “Key Resolve” military drill, which began Monday.

An official said the government tried to use the channel to contact the North to gain permission for 726 South Koreans looking to visit Gaeseong. There was no response.

According to the official, it remains uncertain whether 242 South Korean visitors would return home from Gaeseong Monday afternoon as scheduled.

The Unification Ministry said that 572 South Koreans were at the Gaeseong Industrial Complex as of Monday.