SEOUL — North Korea fired two short-range ballistic missiles off its east coast on Monday, in its fourth weapons test in a month.

The test came after the country fired two ballistic missiles from train cars on Friday, hours after it warned of “stronger and certain reaction” if the United States helped impose more sanctions in response to the North’s recent series of missile tests.

​In response, the United States blacklisted five North Korean officials active in China and Russia who American officials said had been involved in procuring goods for the North’s nuclear weapons and missile programs.

Multiple Security Council resolutions ban North Korea from developing or testing ballistic missile technologies or technologies used to make and deliver nuclear weapons.

​North Korea has since resumed testing mostly short-range ballistic missiles, and Mr