President Trump Donald John TrumpBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Pelosi: Trump Supreme Court pick 'threatens' Affordable Care Act MORE late Saturday night ordered flags outside the White House and other federal buildings be flown at half-staff to honor the victims of the shooting at a Pittsburgh synagogue.

Trump issued a proclamation calling for flags at military posts, public buildings, embassies, consular offices and federal buildings abroad be lowered to half-staff out of "solemn respect" for the victims of Saturday's shooting at the Tree of Life Synagogue, where 11 people were killed.

Flags will remain at half-staff until sunset on Wednesday.

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Eleven people were killed and six others were wounded when a gunman entered Sabbath services and opened fire. The suspect, Robert Bowers, carried a rifle and three handguns and shouted anti-Semitic slurs as he entered the house of worship, police said.

It is believed to be the deadliest attack on the Jewish community in American history, according to the Anti-Defamation League.

Bowers, 46, was charged with 11 counts of criminal homicide, six counts of aggravated assault and 13 counts of ethnic intimidation. Authorities said he told police as he was being treated for injuries upon his arrest that he wanted all Jews to die.

Trump condemned the attack as "an assault on humanity."

"It will require all of us working together to extract the hateful poison of anti-Semitism from our world. This was an anti-Semitic attack at its worst," Trump said during a rally Saturday night.