The shooting happened around 3.15 am local time.

The agents sustained non-life-threatening injuries, broadcaster KSDK reported. One of them was shot in the shoulder, and the other in the leg.

"The incident is not directly related to the Ferguson protests," FBI spokeswoman Rebecca Wu said in a brief statement, as quoted by Reuters.

Roadblocks have been set up as a result of the shooting.

Currently, there is police presence around the local Barnes-Jewish Hospital. However, it isn’t clear whether the FBI agents remain there.

It comes as around 2,000 National Guard forces were deployed in the St. Louis area to help security forces deal with the second night of unrest over the Ferguson fatal shooting of 18-year-old Michael Brown by white police officer Darren Wilson.