Gregory Korte

USA TODAY

WARSAW — President Obama signed a proclamation Friday lowering flags to half-staff at the White House and throughout the government in memory of the police officers killed in Dallas.

Flags will remain lowered until sunset Tuesday, The sniper-style attack that killed five police officers and injured seven others made Thursday the deadliest day for U.S. law enforcement since Sept. 11, 2001.

It;'s the 67th time Obama has ordered flags at half-staff, an act he has performed more than any other president, according to a USA TODAY analysis after the terror attack in Orlando last month.

Obama has ordered flags at half-staff more than any president in history

By the time flags are raised again on Sunday, the Obama White House will have been under a lowered flag for 162 days of his presidency.

Under Obama, mass shooting victims are frequently memorialized with lowered flags, including five incidents in the last year: Chattanooga, Tenn., Roseburg., Ore., San Bernardino, Calif., Orlando and Dallas. Two international terror incidents in Paris and Brussels have also been commemorated.

As required by law, Obama also lowers flags each year for National Police Officers Memorial Day.

Earlier Friday, Obama called the Dallas shooting a "vicious, calculated and despicable attack on law enforcement."

Obama: Dallas police shootings were 'vicious, calculated and despicable'

"I believe I speak for every single American when I say we are horrified over these events, and we stand united with the people and the police department in Dallas," he said.

Obama signed the proclamation while in Warsaw, where he's attending the NATO Summit.