South Korea’s Defense Ministry said Friday night that the multiple unidentified aircraft flying over the sky was a successful test of its solid-fuel space rocket.

The test flight is a follow-up to another launch conducted on March 30. The ministry added that the launch was conducted to strengthen national defense capabilities in areas like independent space-based surveillance and reconnaissance. The ministry also apologized that it couldn’t inform people in advance.

At around 6 p.m., strange rainbow-colored lights were spotted in the sky in several parts of South Korea, including Seoul and parts of Gangwon Province, Gyeonggi Province, and South Chungcheong Province.

The meandering path and color of the rocket caused some witnesses to initially speculate it was a UFO, until the ministry made an announcement.

South Korea launched a solid-fuel space rocket for the first time in March, as part of a project to develop civilian and military surveillance satellites. The agency conducted the launch for Defense Development in Taean, South Chungcheong Province.

The March launch was the first test since South Korea and the United States agreed last year to end restrictions on the country’s ballistic missile and rocket development.