Commanders at two U.S. military bases in Delaware and Colorado tightened security levels this week, in one case after suspicious vehicles were observed at the perimeter.

The Newcastle Air National Guard base in Delaware increased its security Wednesday, the Pentagon said. 

The air base took the precaution after different vehicles approached its gate, then left, according to The Associated Press. 

In at least some of five incidents at the base near Wilmington, an individual asked for directions. In one case, the car turned around before reaching the main gate, the AP said. 

{mosads}NBC reported that U.S. and counterterrorism officials described those incidents as potential “probes” of the base’s security. Officials feared the base might have been under surveillance. 

A senior defense official told NBC that an employee entered the base and spotted four individuals hanging around the base who “appeared to be Muslim.” 

Base spokesman Col. Len Gratteri told the AP that it’s not uncommon for people to get lost, but that the frequency raised suspicions. 

The base’s 166th Airlift Wing posted a message on its Facebook page Tuesday, cautioning those on base to be vigilant and to report suspicious activity. 

Separately, Fort Carson in Colorado raised its security level, but the Pentagon did not release additional information in that case.

The heightened security measures come after last week’s terrorist attacks in Paris, where individuals inspired by al Qaeda and ISIS — at least one of whom traveled to Yemen to train with al Qaeda in the Arabian Peninsula — killed 16 people. 

The Pentagon said it had to strike a difficult balance between taking protective measures and being careful not to profile certain races. 

“There’s a very fine line we have to walk. We depend on our young service members to aggressively yet professionally protect our installations and personnel,” Army Col. Steve Warren said Wednesday. 

“It’s very important that we continue to ensure their professionalism is the highest,” he said. 

“Yes, there are occasions when they perhaps are overzealous. We try to quickly make these corrections to ensure that our personnel are operating very professionally,” he said.