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Three people were injured Wednesday when intruders in an SUV tried to ram through a barrier at the Maryland military base where the National Security Agency is headquartered — and gunfire broke out, officials said.

But the motive for the incident at Fort Meade, which erupted around 7 a.m. ET, remains a mystery, FBI Special Agent in Charge Gordon Johnson said.

"We don't believe there is a nexus to terrorism. We believe this was an isolated incident," Johnson said. "We are still trying to figure out why they were there."

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The driver of the vehicle, an NSA police officer and a civilian who happened to be at Security Gate 1 when the shooting started were hospitalized, Johnson said.

"At this point we don't believe any of the injuries were the result of gunfire," he said.

Neither the NSA officer nor the civilian suffered "life threatening injuries," Johnson said. The condition of the driver, however, was not immediately known, he said.

The two other men who were with the driver of the black SUV were in custody and being questioned by investigators, said Johnson, who did not identify them.

Earlier, aerial footage obtained by NBC Washington appeared to show a black SUV with bullet holes in its windshield — and deployed airbags — that looked to have crashed into a concrete barrier.

At least one handcuffed man was on the ground, surrounded by police, NBC Washington said.

In the wake of the shooting, the Maryland State Police closed a nearby major highway in both directions, causing massive traffic tie-ups and turning the morning commute into a nightmare.

This is not the first incident to happen at an NSA security gate. In March 2015, two unauthorized people tried to enter with a stolen SUV. NSA police fired at the vehicle, killing one suspect and injuring the other, NBC Washington reported.