A fire that burned a Clackamas apartment building to the ground was ruled arson Saturday.

Clackamas County crews evacuated neighbors from a four-alarm apartment fire that rendered the building uninhabitable Friday, officials said.

Slideshow: Flames engulf apartment

It happened at the Clackamas Heights apartments on Southeast Monroe, near 82nd Avenue, before it spread to a building. It’s located in a large complex of free standing, separated buildings.

There were no suspects immediately identified, police said.

The Red Cross said out of the 12 units, ten families -- 20 people total -- were displaced. Ten apartment units were destroyed.

There were no reports of injuries.

Crews originally thought the fire broke out in some brush, but the cause was under investigation.

Flames could be seen licking through holes in the roof as crews attacked from different side of the building. The building eventually burned to the ground, leaving not much more than black debris and ash.