Amanda Knox has been held in prison for almost four years for the murder of Meredith Kercher (Reuters)

An Italian appeals court has thrown out Amanda Knox's murder conviction and ordered the young American freed after nearly four years in prison for the death of her British roommate. Her co-defendant, Italian Raffaele Sollecito, also was cleared of killing 21-year-old Meredith Kercher in 2007.

Knox collapsed in tears after Monday's verdict overturning her 2009 conviction was read out. The Kercher family looked on grimly and a bit dazed as the verdict was read out by the judge after 11 hours of deliberations by the eight-member jury.

Outside the courthouse, some of the hundreds of observers shouted "shame, shame"!

Yet inside the frescoed courtroom, Knox's parents, who have regularly traveled from their home in Seattle to Perugia in Italy to visit the 24-year-old over the past four years, hugged their lawyers and cried with joy.

"We have been waiting for this for four years," Giulia Bongiorno, one of Sollecito's lawyers, said.

After the acquittal, Victoria Nuland, the state department spokeswoman, said: "The US appreciates the careful consideration of this matter within the Italian judicial system."

She further said the US embassy in Rome would continue to provide "appropriate consular assistance" to the American and her family.

Although she was cleared of murder and sexual assault, Knox was found guilty of slander for accusing bar owner Diya "Patrick" Lumumba of carrying out the killing.

The judge set the sentence at three years, meaning for time served. Knox has been in prison since November 6, 2007.

"We have won the battle, but not the war," Luciano Ghirga, one of Knox's lawyers, said, as prosecutor Giuliano Mignini promised to lodge an appeal with Italy's highest appeal court to "ensure that justice is done".

Should the prosecution team launch a final appeal, as appears likely, it would probably have to be held in absentia as the US does not normally extradite its citizens abroad for prosecution.

At the original trial Knox was sentenced to 26 years in prison for the murder and Sollecito, her former boyfriend, to 25 years.

The 21-year-old Kercher was found half-naked in a pool of blood on the floor of her bedroom in the cottage she shared with Knox. Her body was covered in knife wounds and bruises and investigators found traces of a sexual assault.

Rocco Girlanda, a local lawmaker, who befriended Knox and published a book of interviews with her last year, told reporters outside the prison gates that Knox would take a commercial flight for the US on Tuesday.

She was driven back to the Capanne prison near Perugia and discharged a short time later.

Source: Agencies