North Korea has fired two short-range missiles into the Yellow Sea.

A Seoul government official said the North fired what appeared to be two Styx missiles into the Yellow Sea on Tuesday afternoon. The official said the missile firing is most likely a part of a regular military drill as the North Korean military usually conducts military exercises at this time of the year.

A South Korean military official said the missiles were not ballistic ones, but either anti-ship Styx missiles or KN-02 missiles, which are usually fired during military training.

In March, North Korea fired three Styx missiles from a naval vessel in the Yellow Sea and again fired a similar type of missile in May.

Styx missiles were developed by the former Soviet Union. Old models have a range of 46 kilometers while new models have a range of 80 kilometers.

Observers say the missile firing seems to be a part of a regular military training. However, some also raised the possibility that the North made the move to pressure the United States in nuclear negotiations.