SEOUL, South Korea — North Korea fired a second ballistic missile into the sea off the coast of South Korea on Monday, the South Korean military said.

The military said in a statement only that the launch was made Monday morning without giving further details.

The launch came hours after South Korea reported North Korea conducting a short-range ballistic missile test into the sea in a resumption of its weapons testing activities.

Observers said the North’s back-to-back launches were likely a protest against the moves by South Korea and the United States to bolster their nuclear deterrence plans in the face of North Korea’s evolving nuclear threats.