President Barack Obama has ordered flags lowered to half-staff to honor the 12 police officers and two civilians who were shot in an attack in Dallas.

Obama’s proclamation Friday applies to American flags flown at the White House and on all public buildings and grounds, military installations and Navy vessels. It extends through sunset Tuesday, July 12.

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Gov. Greg Abbott ordered Texas flags to be flown at half-staff statewide during the same time period to honor the victims. Five of the officers were killed. The other seven and the two civilians were wounded.

On Friday, Obama said America is “horrified” by the shootings, which have no possible justification. He called them “vicious, calculated and despicable.”

Speaking from Warsaw, Poland, where he was meeting with leaders of the European Union and attending a NATO summit, the president asked all Americans to pray for the fallen officers and their families.