South Korea conducts military exercises near the border with North Korea on Wednesday.
At the White House on Friday, spokesman Jay Carney said the United States "would not be surprised" if North Korea actually carries out a missile test.
"We have seen them launch missiles in the past, and the U.N. Security Council has repeatedly condemned them as violations of the North's obligations under numerous Security Council resolutions, and it would fit their current pattern of bellicose, unhelpful and unconstructive rhetoric and actions," Carney said.
If the North Koreans do launch a missile, the U.S. would have to decide whether to shoot it down. On the eve of a launch in 2006, then-Defense Secretary Donald Rumsfeld said U.S. forces would do so only if the missile were headed toward U.S. territory.
After the North Koreans shelled a South Korean military base in 2010, however, U.S. and South Korean leaders resolved to respond more aggressively to such incidents. They drew up what they called a counterprovocation plan, and this year they knew the plan might be put to a test.
One Plan, Three Messages
The U.S. and South Korea stage joint military exercises every year around this time, and North Korea always gets upset. This year, there's a new leader in the North, determined to make an impression. So the U.S. and South Korea decided it was important to "signal" their readiness to respond to hostile action and the exercises included an especially dramatic show of force with stealth bombers.
The reaction from the North has been especially aggressive.
Gen. Walter Sharp, who until last year was the commander of U.S. forces in Korea, says the whole sequence of events shows how challenging it is to deal with all the demands, contingencies and the risks on the Korean Peninsula.
"That's why there's been a lot of effort over the past two and a half years now to build this counterprovocation plan," Sharp says. "Because that's a hard balance of a strong response — don't escalate, but be prepared to go to war."