The announcement came amid reports of heightened activity at the North's nuclear test site, and at a missile battery, although the South Korean government denied suggestions that a fourth nuclear test was imminent.
No Justification for Withdrawal
South Korea's unification ministry said the unilateral withdrawal "cannot be justified in any way, and North Korea will be held responsible for all the consequences."
"The [South] Korean government will calmly but firmly handle North Korea's indiscreet action, and we will do our best to secure the safety of our people and the protection of our property," a ministry spokesman said.
More than 300 South Koreans have left Kaesong and returned to the South since North Korea banned access last week. The unification ministry said 475 South citizens were still staying at the complex as of Monday.
"How the situation will develop in the days ahead will entirely depend on the attitude of the South Korean authorities," said Kim, who blamed the pull-out on "military warmongers" who had affronted the North's "dignity."
The Korean peninsula has been locked in a cycle of escalating military tensions since the North's third nuclear test in February, which drew toughened United Nations sanctions.
Activity at Nuclear Test Site Labeled 'Routine'
The South's defense ministry said Monday that activity detected at the North's Punggye-ri atomic test site was "routine" and should not be interpreted as final preparation for another detonation.
"There is no indication that a nuclear test is imminent," ministry spokesman Kim Min-Seok said, while adding that the North consistently maintained Punggye-ri at a state of test-readiness.
The South's unification minister had appeared to confirm a report by the JoongAng Ilbo daily, which cited intelligence reports of stepped-up activity at the site. But he then insisted his remarks had been misinterpreted.
The U.N.'s atomic watchdog chief -- Yukiya Amano, director general of the International Atomic Energy Agency -- on Monday called North Korea's drive to restart a nuclear site at Yongbyon "troubling" and said his team could not detect whether the regime planned a new nuclear test due to a lack of access.
North Korea's bellicose rhetoric has reached fever pitch in recent weeks, with near-daily threats of attacks on U.S. military bases and South Korea in response to ongoing South Korea-U.S. military exercises.
Intelligence reports suggest Pyongyang has readied two midrange missiles on mobile launchers on its east coast, and plans a test-firing before the April 15 birthday of late founding leader Kim Il-Sung.
A missile launch would be highly provocative, especially given the strong rebuke the North's sole ally China delivered on Sunday.
"No one should be allowed to throw a region, even the whole world, into chaos for selfish gains," President Xi Jinping told a high-powered business forum in southern China.
