A Frankfurt airport security officer approaches the U.S. military bus where at least four people were shot Wednesday.

[Update 1:40 p.m. ET] President Barack Obama said Wednesday he was “saddened and outraged” by an attack in Germany that killed two Americans and wounded two others. “We will spare no effort in learning how this outrageous attack took place,” Obama said, adding that American officials are working with German authorities to investigate.

[Update 11:19 a.m. ET] Two people were shot and killed Wednesday in an incident involving a U.S. military bus at Frankfurt Airport in Germany, a police spokesman said.
Another person is severely wounded, Juergen Linker told CNN, and one person is in custody.
A U.S. military official said initial reports were that two people had been killed, including the driver of the bus.
It is not clear if the driver was German or American, or military or civilian.
Two others are wounded, said the source, who is not authorized to speak publicly about the incident.
The troops killed and injured are U.S. Air Force airmen from Lakenheath base in the United Kingdom, the U.S. official said, emphasizing that the information was only preliminary.
They were security forces on their way to a deployment, the source said, without saying specifically where they were heading.
They were flying commercial, not on a military plane, according to the source.
It’s believed the German police have a young Kosovo national in custody, the U.S. official said.
The U.S. military base at Ramstein in Germany regularly runs shuttles to Frankfurt for commercial flights.
[Update 10:52 a.m. ET] Two people were shot and killed Wednesday in an incident involving a U.S. military bus at Frankfurt airport in Germany, a police spokesman said.
Another person is severely wounded, Juergen Linker told CNN, and one person is in custody.
The U.S. military did not immediately comment on the incident.
[Original post, 10:47 a.m. ET] Two U.S. soldiers were shot and killed Wednesday at Frankfurt airport, Germany’s busiest airport, a police spokesman said.
There were conflicting reports as to whether the shooting took place inside a terminal or aboard a shuttle bus.