North Korea test fired four, short-range missiles into the sea on Thursday, South Korea's Defense Ministry said according to Reuters.
The missiles were fired from the country's eastern coast at around 5:42 local time (8:42 GMT), Reuters reported. The weapons had an estimated range of 125 miles, a South ministry spokesman told The Guardian. No official reason for the test was given.
"Our military will maintain tight vigilance in preparation for additional launches or any military provocation from the North," the ministry spokesman told The Guardian.
According to the South Korean news outlet Yonhap, the type of missiles used are most likely Scud short-range missiles, Reuters reported. Their range is 200 miles, making them capable of reaching South Korea but not Japan.
The U.S. and South Korea began their yearly joint military exercises a few days prior to Thursday's test, Reuters reported. North Korea often claims the exercise is a cover to prepare for war.
North Korea was also upset earlier this month after the U.S. sent a B-52 bomber, capable of a nuclear strike, over South Korea, Reuters reported.
North Korea frequently carries out missile tests to the point where the U.S. does not always consider them a threat.
Army Colonel Steven Warren, a Pentagon spokesman, told Reuters the U.S. kept tabs on Thursday's missile launch. The missiles were not aimed at a specific target, and landed off the country's coast. Warren said they did not see the launch as instigative.
"This one actually we do not, frankly. We've seen these types of missile tests fairly regularly. It's a short-range Scud missile, which they are allowed to test," Warren told Reuters.
"Nevertheless, we always call on the (North) Koreans to refrain from provocative actions," Warren added.
Warren also said the launch appears to have been just an unexpected missile test.