The move increases pressure on Pyongyang even as delegations of old soldiers from Commonwealth countries finished tours of their former battlefields.
Tension on the divided peninsula has been simmering for weeks, but the South warned of "grave consequences" with the continued closure of the sprawling factories at Kaesong, North Korea.
South Korea set Friday as a deadline for talks on the future of the joint venture.
North Korea early this month barred South Koreans from crossing the border and entering the factory and later withdrew the 53,000 northern workers who operate the assembly lines.
The complex is owned and managed by South Korean companies, but employs northern workers and has been idle for a month in a protest by Pyongyang over increasing United Nations sanctions.
Since 2004, it has survived many political crises.
Canada's veterans affairs minister marvelled at how calm and normal life appeared to be in Seoul on Thursday, despite the pressure and threats from Kim Jong Un's regime to unleash nuclear weapons on its southern neighbour.
Steven Blaney said at no point did he consider cancelling — or cutting short — a visit by three dozen veterans of the 1950-53 conflict, but has received regular security updates from the Canadian embassy and South Korean officials.
He said he admires the way the South Korean economy and people have thrived under such stress.
Officials with the South Korean military, in briefings to Canadian veterans, say from their observation posts they've seen North Korean troops taking to the fields to begin the planting season — a sign of the immense strain the tottering northern economy faces.
The U.S. has said it is prepared for Pyongyang to conduct another medium-range missile test — or even a fourth nuclear weapons experiment.
Blaney held a bilateral meeting Thursday with his South Korean counterpart and says he'll be able to give the federal cabinet a clear sense of conditions on the ground, if needed.
The South Koreans understand that Canada is behind them, he added.
"This journey we are living this week is not just about what took place 60 years ago, but it is about the present and the future of Korea and Canada," Blaney said.
This year marks the 60th anniversary of the truce that ended the Korean War.
Hopes that a diplomatic settlement of the latest crisis might be in the offing have dimmed somewhat, even though the North has dialed back its angry rhetoric.
Pyongyang is demanding recognition as a nuclear state — something the U.S. is not prepared to grant under any circumstances.
Washington is demanding that North Korea dismantle its existing nuclear weapons as a condition for negotiations.
North Korea signed a deal in 2005, promising to disarm its warheads in exchange for food, but later backed out.