( CNN ) -- Hundreds of South Koreas were left in limbo after North Korea shut its borders Monday at the start of joint military exercises between the United States and South Korea . U.S. troops have started joint military exercises with their South Korean counterparts . When Pyongyang took the action , 573 South Koreans were staying at the Kaesong industrial complex , north of the demilitarized zone , South Korea 's Yonhap news agency reported . Many of the stranded South Koreans work at the complex , which is a joint project between the Koreas . `` The South Korean government is closely monitoring the situation and preparing for all contingencies , '' said Kim Ho-nyun , a South Korean Unification Ministry spokesman . `` We emphasize that currently the first priority is the safety of our citizens . '' Eighty South Koreans had applied to cross the border into South Korea on Monday , Kim said , but had not been cleared to do so . `` We are also not certain what will happen to the South Koreans that want to cross tomorrow as well , '' he said . The cross-border developments came as North Korea said it would retaliate if a `` satellite '' launch from its northeastern coast were intercepted , with the communist nation saying interference would `` mean a war . '' `` Shooting our satellite for peaceful purposes will precisely mean a war , '' a spokesman for the North Korean army said in a statement carried by the state-run Korean Central News Agency ( KCNA ) . U.S. and South Korean officials have said that North Korea appears to be preparing to test-fire its long-range missile , the Taepodong-2 , under the guise of launching a satellite into space . The missile is thought to have an intended range of about 6,700 kilometers ( 4,200 miles ) , which -- if true -- could give it the capability of striking Alaska or Hawaii . North Korea 's bellicose announcement came on the first day of annual joint military drills between South Korea and the United States . `` We have said several times that the U.S.-South Korean military exercises are annual defensive exercises , '' Kim said . `` We again urge North Korea to maintain the agreed stance of mutual respect and to stop its verbal attacks and actions that are raising tensions on the Korean peninsula , '' he said . The North said it has shut its borders to `` any enemies '' and has cut off `` the North-South military communications in order to guarantee the security . '' North Korea said the military phone lines with the South , the last remaining communications channel , will remain closed until the 12-day military exercises end on March 20 , according to Yonhap . Kim said his government is urging North Korea `` to immediately retract this measure and to allow the smooth flow of personnel and communication . '' On Saturday , U.S. envoy Stephen Bosworth said he wants dialogue with North Korea , but he also spoke against North Korea 's move to go forward with a launch , saying it would be `` ill-advised . ''
573 people staying at Kaesong industrial complex , north of demilitarized zone . 80 South Koreans not cleared to cross the border into South Korea Monday . Follows vow to retaliate from N. Korea if its satellite launch is intercepted . Comment: