North Korea has test-fired four short-range missiles into the sea off its east coast.
South Korea’s Defence Ministry said they had an estimated range of 200 kilometres.
“Our military will maintain tight vigilance in preparation for additional launches or any military provocation from the North,” a Ministry spokesman said.
The news coincides with join South Korea-US military exercises, which the North had warned against.
The South Korea-US drills began on Monday.
This year, they overlapped with the end of the first reunion for more than three years of families divided by the Korean War.
Pyongyang had initially insisted the joint exercises be postponed until after the reunion finished on Tuesday, but Seoul refused and – in a rare concession – the North allowed the family gathering on its territory to go ahead as scheduled.
North Korea carries out short-range missile tests on a fairly routine basis, and has used them before to display its anger at the annual military exercises.
Observers said these tests are unlikely to trigger a significant rise in military tensions.
