WASHINGTON — President Barack Obama said today he’s “saddened and outraged” by the shooting in Frankfurt, Germany, that killed two U.S. Air Force personnel and injured two others.

The president says the U.S. will spare no effort in finding out how the “outrageous” act took place and will ensure the perpetrators are brought to justice. It happened today on a bus outside the Frankfurt airport. Obama called it a tragedy.

The president made his brief comments in a surprise appearance in the White House press briefing room during the regular daily briefing.

The U.S. Air Force in Britain says the two airmen killed and two others wounded in the Frankfurt airport shooting were based in the U.K.

A spokesman for Air Force at Lakenheath airfield confirmed all four were from the military base in eastern England.

Lakenheath is home to the 48th Fighter Wing, the United States’ only F-15 fighter wing.

Its website says the base employs some 4,500 active-duty military members, as well as 2,000 British and U.S. civilians.