Updated 11:22 PM ET
(CBS News) THE PENTAGON - There were more threatening words -- and actions -- Wednesday from North Korea.
The country says it's leadership has approved plans for a nuclear strike on the United States. They have also put up a roadblock at a border crossing, stopping South Korean workers and supplies from reaching the Kaesong industrial park, where textiles and electronics are made. The Associated Press reported that the South Korean workers were again turned away from the Kaesong factories on Thursday morning.
The industrial park at Kaesong was the one slender thread of evidence that two countries at each others' throats could still do business. Now, in what one U.S. official called "the provocation of the day," this last point of contact between the two countries has been cut off. It's added to North Korea's warlike posturing, which Defense Secretary Chuck Hagel said cannot be ignored.
"It only takes being wrong once, and I don't want to be the secretary of defense who was wrong once. So we will continue to take these threats seriously," Hagel said.
Last week, North Korea's dictator Kim Jong Un ordered his missile units to prepare for attacks on the U.S. itself in retaliation for an annual exercise involving American and South Korean forces.
"Some of the actions they've taken over the last few weeks present a real and clear danger and threat to the interests, certainly of our allies," Hagel said.
The Pentagon announced Wednesday it is sending a battery of air defense missiles to the Pacific island of Guam, which recently served as a base for B-52 bombers that flew over South Korea as part of that annual exercise. Next week the exercise will include an amphibious landing and live fire drills by U.S. Marines.
There are still no troop movements to indicate North Korea is about to attack either the U.S. or South Korea. But with all this harsh rhetoric, there is concern a minor incident, such as an exchange of gunfire over disputed fishing waters, could quickly spin out of control.