A bullet hole from a gun battle in Ciudad Juarez is seen on the wall of El Paso Assistant City Manager Pat Adauto’s office in El Paso, Texas, in this June 30 file photo. Juarez and the area where the gun fight took place can be seen out the window of Adauto’s office.

El Paso, Texas ? The first bullets struck El Paso’s city hall at the end of a work day. The next ones hit a university building and closed a major highway.

Shootouts in the drug war along the U.S.-Mexico border are sending bullets whizzing across the Rio Grande into one of the nation’s safest cities, where authorities worry it’s only a matter of time before someone gets hurt or killed.

At least eight bullets have been fired into El Paso in the last few weeks from the rising violence in Ciudad Juarez, Mexico, one of the world’s most dangerous places. And all American police can do is shrug because they cannot legally intervene in a war in another country. The best they can do is warn people to stay inside.

“There’s really not a lot you can do right now,” El Paso County Sheriff Richard Wiles said. “Those gun battles are breaking out everywhere, and some are breaking out right along the border.”

Police say the rounds were not intentionally fired into the U.S. But wildly aimed gunfire has become common in Juarez, a sprawling city of shanty neighborhoods that once boomed with manufacturing plants. It’s ground zero in Mexico’s relentless drug war.

More than 6,000 people have been killed there since 2008, when the Sinaloa and Juarez cartels started battling each other and Mexican authorities for control of the city and smuggling routes into the U.S. Nationwide, more than 28,000 people have been killed since President Felipe Calderon launched his offensive against the cartels shortly after taking office in December 2006.

Until now, communities on the U.S. side of the border have been largely shielded from the violence raging just across the river. But the recent incidents are the first time that live ammunition has landed in American territory.

On Saturday, as gunmen and Mexican authorities exchanged gunfire in Juarez, police in El Paso shut down several miles of border highway. Border Patrol spokesman Doug Mosier said his agency asked for the closure — a first since the drug war erupted — “in the interest of public safety.”

No one was injured on the U.S. side, but one bullet came across the Rio Grande, crashed through a window and lodged in an office door frame at the University of Texas at El Paso. Police are also investigating reports that another errant round shattered a window in a passing car. Witnesses at a nearby charity said at least one bullet hit their building, too.

El Paso police spokesman Darrel Petry said authorities have only confirmed the single bullet found at the university, but it is possible that several other shots flew across the border.

“As a local municipality, we are doing everything we can,” Petry said. “Looking where we’re at, the community we live in, that’s all we’ve got. It’s the reality of life here in El Paso for right now.”

Officers say the types of bullets used in the drug war can travel more than a mile before falling to the ground.

In Saturday’s shooting, the bullet that hit the campus building may have flown just under a mile before lodging in a door jamb.

Back in June, at least seven shots fired from Juarez flew more than half a mile before hitting City Hall.

In some places, El Paso is separated from Juarez by little more than a few yards of riverbed.