North Korea fired a ballistic missile toward the sea on Friday, Seoul officials said, as its rival South Korea was wrapping up an annual military drill that the North views as an invasion rehearsal.

South Korea’s Joint Chiefs of Staff said in a statement the missile flew toward North Korea’s eastern waters but gave no further details including how far the weapon flew.

The launch, the latest in a series of weapons tests by North Korea in recent weeks, came on the final day of South Korea’s annual 12-day “Hoguk” field exercises, which also involved an unspecified number of U.S. troops this year.

The South Korean and U.S. air forces plan to conduct a large-scale training next week.

North Korea sees such regular drills by Seoul and Washington as practice for launching an attack on the North, though the allies say their exercises are defensive in nature.

Friday’s launch came four days after the rival Koreas exchanged warning shots along their disputed western sea boundary, a scene of past bloodshed and naval battles.

The launch also came after U.S. Deputy Secretary of State Wendy Sherman during a visit to Tokyo this week issued a warning over North Korea’s escalating provocations and reiterated that the U.S. would fully use its military capabilities, “including nuclear,” to defend its allies Japan and South Korea.

There are also concerns that the North could up the ante in the coming weeks by conducting its first nuclear test since 2017. Rafael Grossi, chief of the International Atomic Energy Agency, said Thursday that a new nuclear test explosion by North Korea “would be yet another confirmation of a program which is moving full steam ahead in a way that is incredibly concerning.”

He said the U.N. agency has been observing preparations for a new test, which would be the North’s seventh overall, but gave no indication of whether an atomic blast is imminent.