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Rep. Gabrielle Giffords announced Sunday that she has "more work to do" on her recovery after an assassination attempt and will resign from her congressional seat this week.

In a video release posted on her website and tweeted from her Twitter handle, the congresswoman said that she is getting better but wants to do what's right for her constituents.

"Arizona is my home, always will be. A lot has happened over the past year. We cannot change that, but I know that on the issues we fought for we can change things for the better: Jobs, border security, veterans. We can do so much more by working together," she says in the two-minute video.

"I don't remember much from that horrible day, but I will never forget the trust you placed in me to be your voice. Thank you for your prayers and for giving me time to recover. I have more work to do on my recovery so to do what is best for Arizona, I will step down this week," she says.

Giffords, D-Ariz, was shot in the head on Jan. 8, 2011, while holding a town hall meeting in Tucson outside a grocery store. She was one of 13 people injured. Six others, including her aide, Gabe Zimmerman, were killed in the assault. The alleged gunman, Jared Loughner, is being treated with anti-psychotic drugs in a prison hospital to determine whether he will become fit to stand trial.

The attack on Giffords led to calls for more civility in Congress, including from President Obama who attended a memorial service in Tucson for the fallen. Giffords returned to Congress just once during the last year -- to vote on a debt ceiling deal that had bitterly split the Congress and White House.

Giffords and her husband, astronaut Mark Kelly, had announced recently that Giffords would decide soon whether to run for reelection. In a note to Giffords' staff and obtained by Fox News on Sunday, Kelly said, "While Gabby was hopeful that she would return to work this year, she has recently determined that it will take more time."

"We wish things were different," he added. "We wish the tragedy of January 8th hadn't happened. We wish that six innocent lives weren't lost. ... But it is our mission to remain positive and reflect on just how lucky our family is better. Gabby is getting better and her can-do spirit will lead her towards a life of success and happiness."

News of Giffords' decision spread quickly. House Democratic leader Nancy Pelosi issued a statement saying that Giffords "has been a true bright star."

"Gabby's message of bipartisanship and civility is one that all in Washington and the nation should honor and emulate," said Pelosi, who was informed of the decision ahead of the announcement.

Sen. Kirsten Gillibrand, D-N.Y., one of the congresswoman's close friends on Capitol Hill, issued a statement noting that Giffords demonstrated to the world that she is "an extraordinary woman of fierce drive, determination and courage."

"Gabby made the right decision for her and her family, but this is just the beginning of the next chapter of her story," Gillibrand said. "I know that Gabby will find other ways to fulfill her calling of public service and continue to lead and inspire the nation."

Republicans also expressed their appreciation for Giffords.

"We salute Rep. Giffords for her service, & for the courage & perseverance she has shown in the face of tragedy. She will be missed," tweeted House Speaker John Boehner.

In the video, Giffords is seated, wearing red. Interspersed in the video of her addressing the camera are shots of Arizona and her talking to constituents as well as pictures of her walking with Kelly.

"I'm getting better. Every day my spirit is high. I will return and we will work together for Arizona and this great country. Thank you very much," she says.

In a formal statement released by her office, Giffords, who was elected in November 2006, said she was proud that her district included Tombstone, the "town too tough to die."

Giffords will submit her letter of resignation later this week to Boehner and Arizona Gov. Jan Brewer. Brewer will set the date for a special primary and general elections within 72 hours of Giffords' resignation. Both votes will likely be held by the end of June. Another regularly scheduled general election will be held in November.

As one of her last acts as a member of Congress, Giffords will attend the State of the Union speech Tuesday evening at the Capitol.