Several Valley residents reported seeing strange red lights in the sky on Monday night and the cause of the lights remains a mystery.

Arizona Republic reporter Anne Ryman, who lives in Deer Valley, reported seeing four lights in a square shape that eventually became a triangular shape. The lights were moving to the east and they disappeared one by one. She said the lights were visible for about 13 minutes at about 8 p.m..

One north Phoenix resident, who wished to remain anonymous, said he saw four or five red lights lined up in a straight line and spaced apart evenly. The lights slowly moved east and became dimmer as the witness watched. He said the last light remained in the sky the longest. Then three jets came from the west and traveled in the direction of the red lights.

An official from Luke Air Force Base stated that they did not have any aircraft in the sky Monday night and that the lights were not part of any Air Force activities.

The Deer Valley airport officials said that the lights were not from any aircraft at that airport.

Ian Gregor, a spokesman for the Federal Aviation Administration said that air traffic controllers at Sky Harbor Airport also witnessed the lights, but they do not know the cause.

The incident is similar to the "Phoenix Lights" seen on March 13, 1997. Thousands of residents reported seeing a mile-wide, v-shaped formation of lights over the Valley. In that case the lights appeared about 7:30 p.m. and lasted until 10:30 p.m.