U.S. President Barack Obama and other ranking officials and politicians expressed their shock at the shooting of U.S. Representative Gabrielle Giffords of Arizona on Saturday morning, calling the incident a national tragedy.

"What we do know is that such a senseless and terrible act of violence has no place in a free society. I ask all Americans to join me and Michelle (the first lady) in keeping Representative Giffords, the victims of this tragedy, and their families in our prayers," Obama said in a statement.

"An attack on one who serves is an attack on all who serve," House Speaker John Boehner (R-Ohio) said. "Acts and threats of violence against public officials have no place in our society. Our prayers are with Congresswoman Giffords, her staff, all who were injured, and their families. This is a sad day for our country."

"Congresswoman Giffords is a brilliant and courageous Member of Congress, bringing to Washington the views of a new generation of national leaders," House Minority Leader Nancy Pelosi (D-Calif.) said. "It is especially tragic that she was attacked as she was meeting with her constituents whom she serves with such dedication and distinction."

Janet Napolitano, Homeland Security Secretary and former Arizona governor, said: "There is no place in our society or discourse for such senseless and unconscionable acts of violence."