Knox says news of retrial 'painful'

Amanda Knox said Tuesday it was "painful" to learn she will be retried in Italy for the 2007 murder of her British housemate, but the American insisted on her innocence.

"It was painful to receive the news that the Italian Supreme Court decided to send my case back for revision when the prosecution's theory of my involvement in Meredith's murder has been repeatedly revealed to be completely unfounded and unfair," Knox said in a statement.

Knox and her Italian former boyfriend Raffaele Sollecito -- originally sentenced to 26 and 25 years in prison for killing and sexually assaulting Meredith Kercher in 2007 -- were acquitted on appeal in 2011 after four years in prison.

Both now face a retrial in a Florence court after judges upheld a 2012 prosecution appeal against their acquittals.

Knox, 25, returned home to the US immediately after her release and, should she not return to Italy, will likely be tried in absentia as the United States does not normally extradite its citizens to face legal action.

Knox said "any questions as to my innocence must be examined by an objective investigation and a capable prosecution."

She expressed sympathy for Kercher's family, saying "our hearts go out to them."

"No matter what happens, my family and I will face this continuing legal battle as we always have, confident in the truth and with our heads held high in the face of wrongful accusations and unreasonable adversity," she said.

Earlier, Knox's lawyer Carlo Dalla Vedova told CNN that she was "upset" but "ready to continue, and willing to fight."