Updated

The shooting of Rep. Gabrielle Giffords prompted a massive bipartisan outpouring of support and grief for the Arizona Democrat and her family Saturday as the U.S. Capitol Police advised lawmakers and their aides to be cautious.

In a live statement, President Obama said he had spoken to Arizona Gov. Jan Brewer and offered her the full resources of the federal government. He also said he is sending FBI Director Robert Mueller to oversee the investigation of the shooting.

Giffords is in an intensive care unit following surgery for a gunshot wound in the head at close range. Nineteen people reportedly were shot at Giffords' "Congress on Your Corner" event, including three of the congresswoman's staff in Arizona. At least five of the 19 people died, including U.S. District Judge John M. Roll, one of Giffords' aides and a 9-year-old child. Several are in critical condition at the University of Arizona Medical Center.

Obama said he wasn't surprised that Giffords was meeting with her constituents, "listening to the hopes and prayers of her neighbors."

"That is why this is more than a tragedy for those involved," he said. "It's a tragedy for Arizona and a tragedy for our entire country."

A U.S. Capitol Police spokesman said it was working alongside federal, state and local law enforcement agencies in the investigation but "there is no indication at this time that this event is part of a larger threat against the congressional membership or has a nexus to terrorism."

In the statement, the spokesman added: "The Senate Sergeant at Arms Office is actively involved in monitoring this event, assessing any additional or expanded threats and working with the U.S. Capitol Police. As more information is confirmed it will be provided. In the interim, if members are in a public forum or scheduled to be in a public forum and feel uncertain about their safety, they should contact the U.S. Capitol Police immediately."

Lawmakers from both sides of the aisle have been issuing statements all day expressing shock and horror over the attack.

Rep. Trent Franks, R-Ariz., told Fox News that one of the last things he saw Giffords do was read aloud a portion of the Constitution on the the House floor along with other newly sworn lawmakers. She recited the First Amendment, including the right of the people to peaceably assemble.

"And ironically, when she was out doing her job and exercising her rights under that amendment, some monstrous degenerate shot her down," he said. "And I just want her and her family to know we need to prosecute that individual with the greatest energy to the greatest extent of the law that we possibly can."

He added: "We need to send a message that this free republic is not going to be intimidated by lunatics or by those who would try to destroy our way of life out of making us fearful."

Homeland Security Secretary Janet Napolitano, who is a former governor of Arizona, condemned the shooting and said she has offered all possible assistance to the FBI and local authorities.

"There is no place in our society or discourse for such senseless and unconscionable acts of violence," she said in a statement. "My thoughts and prayers are with Congresswoman Giffords, her family and staff, and all those who were injured in this difficult time."

Although Giffords is a Democrat, she's a former Republican and self-described moderate who isn't afraid to mix it up with members of her own party.

Last year, she criticized the Obama administration for suing Arizona over its controversial law cracking down on illegal immigrants. She also assailed Obama for not sending more National Guard troops and Border Patrol agents to the Mexican border after the killing of a prominent southeast Arizona rancher.

Giffords was one of 19 Democrats this week who didn't vote for House Minority Leader Nancy Pelosi as speaker, after voters returned control of the House to Republicans in November's midterm elections.

But none of the politics made a difference on Saturday. Dozens of statements were released from lawmakers and administration officials in the immediate aftermath, including the two Republican senators from the state, John McCain and Jon Kyl; many in the House leadership from both parties; Obama; Vice President Joe Biden; Attorney General Eric Holder; Republican Arizona Gov. Jan Brewer; former Republican presidential candidates Sarah Palin and Mitt Romney; and many more from around the country. All noted their high regard for and personal relationship to the congresswoman, who in 2002 was the youngest woman ever to be elected to the Arizona state Senate.

Pelosi acknowledged the shooting at the start of a town hall meeting in San Francisco.

"We stand before you with the deepest sadness for the act of violence that was committed against our colleague, Congresswoman Gabby Giffords, her staff, her constituents, and now we know a federal judge as well," she said. "Congresswoman Giffords is a great patriotic American, a representative in Congress of a new generation of leaders, brilliant, patriotic."

An impromptu vigil on Capitol Hill was held Saturday evening.

Prior to that, her opponent in the November election, Jesse Kelly, said he was praying for her recovery.

And while her father Spencer Giffords, told The New York Post in tears that "the whole Tea Party" was against the congresswoman, the Tea Party Express issued a statement saying the "heinous crimes have no place for America."

"And they are especially grievous when committed against our elected officials. Spirited debate is desirable in our country, but it only should be the clash of ideas. An attack on anyone for political purposes, if that was a factor in this shooting, is an attack on the democratic process. We join with everyone in vociferously condemning it," reads a statement from Tea Party Express Chairwoman Amy Kremer.