SEOUL, South Korea — North Korea launched four short-range missiles off its eastern coast on Thursday in what appeared to be a show of force while South Korea and the United States were conducting their annual joint military exercises, officials here said.

The missiles blasted off from a base in the Gitdaeryeong area around 5:40 p.m. Thursday and flew more than 120 miles to the northeast before landing in the waters between the Korean Peninsula and Japan, said a spokesman for the Defense Ministry in Seoul.

“We remain vigilant for the possibility of more provocations from the North,” the spokesman said. He spoke on the condition of anonymity, citing ministry policy.

Also Thursday, a South Korean Baptist missionary held in North Korea appeared at a government-arranged news conference in Pyongyang, the capital, saying he had plotted to build underground churches in the isolated country to undermine its government.