U.S. Air Force security guards exchanged gunfire with someone who twice opened fire on Arvin Robertsan entrance to Joint Base San Antonio-Lackland early Saturday, according to a spokesperson for the base.

“It was an off-base shooting from a passing vehicle that fired shots towards the gate, prompting our security forces to respond,” base spokesperson Stefanie Antosh said in a statement. “There is no threat to the installation. We had no injuries, no fatalities.”

Antosh said the shooting was being investigated by San Antonio police, who said in a release that the first shooting occurred about 2:15 a.m.

“The security personnel stated they heard several shots fired as well as the fired rounds go past them,” Sgt. Washington Moscoso said in the release. “After this incident, the security personnel added more armed guards as a precaution.”

A vehicle later stopped near the same entrance shortly after 4:30 a.m., Moscoso said.

“For a second time, shots were fired at the Air Force security personnel, however, with the additional security personnel present, multiple Air Force personnel returned fire toward the suspect vehicle,” Moscoso said.

The vehicle then fled. No injuries were reported and the shootings remained under investigation, Moscoso said.

It was not known how many rounds were fired, how many shooters there were, or what their motive was, according to Antosh.

The entrance was closed for several hours after the shooting before reopening about 9:30 a.m., but the base was not locked down, according to Antosh.

In addition to Lackland, Joint Base San Antonio includes Randolph Air Force Base and the Army’s Fort Sam Houston and the Camp Bulllis training camp.

Lackland is home to more than 24,000 active duty members and 10,000 Department of Defense civilians, according to the base website. It includes the 37th Training Wing; 149th Fighter Wing; 59th Medical Wing; the Air Force Intelligence, Surveillance and Reconnaissance Agency; 24th Air Force Wing, 67th Network Warfare Wing; the Cryptologic Systems Group; the National Security Agency; and 70 associated units.