President Obama said Wednesday that he is "saddened" and "outraged" by the shooting of a group of U.S. airmen in Germany that left two dead.

U.S. military officials in Europe said Wednesday that two other airmen were injured after a gunman opened fire on an American military bus at the Frankfurt airport. The names of the dead will not be released until their families are informed.

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During a surprise appearance in the White House briefing room, Obama said that the U.S. will do all it can to assist in the investigation.

"I'm saddened and I am outraged by this attack," Obama said.

The president added that Americans are "united" in expressing gratitude to the servicemen who were killed.

According to The New York Times, local media outlets reported that the suspected shooter is a 21-year-old Kosovar. Of the two service members who were wounded, one was seriously injured.

The U.S. "will spare no effort in learning" how the attacks took place, Obama said. Frankfurt police are investigating the shooting.

Obama declined to answer whether the incident was an act of terrorism, telling the White House press corps he would take questions on Thursday when he meets with Mexican President Felipe Calderón.