Update: NBC News confirms that two shots hit the Pentagon.

Police are searching for suspects after two shots struck the Pentagon but did not penetrate, NBC News reported.

The shots, fired at about 4:30 a.m., struck windows on the south side of the building. The windows that were hit are being removed as evidence.

Original story continues below...

WASHINGTON — Police were searching Monday for the source of potential gunshots fired near the Pentagon, though operations were back to normal after they found nothing suspicious, a spokesman said.

Pentagon police officers heard about four or five gunshots around 4:55 am (0855 GMT) fired at or near the south parking lot of the massive Defense Department headquarters, Pentagon Force Protection Agency spokesman Chris Layman told AFP.

They locked down the area, along with all of the Pentagon's entrances before conducting sweeps of the area, including a canine search with local police.

"They did not find anything," Layman said.

"They're investigating it right now, they're not sure what happened right now."

By 6:00 am (1000 GMT), all Pentagon entrances were reopened and operations were back to normal, he added.

With additional reporting by RAW STORY.