President Barack Obama called on Americans to observe a moment of silence Monday at 11:00 a.m. EST to honor the victims of the shootings in Tucson, Arizona.

"It will be a time for us to come together as a nation in prayer or reflection, keeping the victims and their families closely at heart,” the president said in an advisory.

Obama will observe the moment of silence with White House staff on the South Lawn.

Flags are to be flown at half-staff in accordance to the president's proclamation.

Obama's planned trip to Schenectady, New York, on Tuesday to the General Electric energy division is postponed. The trip is expected to be rescheduled, the press advisory said.