Al Jazeera has described the verdict of an Egyptian court a deliberate attack on press freedom after it sentenced three of its journalists to three years in prison.

Egyptian Baher Mohamed and Canadian Mohamed Fahmy are heading back to jail after a retrial found them guilty of "broadcasting false news".

Australian Peter Greste - who was sentenced in absentia - said Saturday's verdict was clearly political.

Mohamed and Fahmy were sentenced to three years in prison after being found guilty by the Cairo court of "aiding a terrorist organisation".

The journalists and Al Jazeera vigorously denied the accusations during the course of the trial.

Keep shouting for us my colleagues I'm sorry. from now on will not be able to keep in touch with you #FreeAJStaff — Baher Mohamed (@Bahrooz) August 29, 2015

Security sources told Egypt's MENA state news agency that Mohamed and Fahmy arrived at Cairo's Tora prison just hours after sentencing.

Greste was also sentenced to three years in jail, having been deported to his home country in February under a new law allowing foreign prisoners to be deported.

The journalists were accompanied by Chadi Abdel Hamid, a student, who was also given a three-year prison sentence, along with Sohaid Saad and Khaled Mohamed, MENA reported.

Baher Mohamed was sentenced to an additional six months for possession of a spent bullet casing.

The journalists had been initially found guilty in June 2014 of aiding a "terrorist organisation", a reference to the Muslim Brotherhood, which was outlawed in Egypt after the army overthrew President Mohamed Morsi in 2013.

Baher Mohamed and Fahmy were on bail in advance of the verdict after they spent 410 days in detention.

Greste was jailed for 400 days.

The Cairo court said on Saturday that the previous time spent in prison will be accounted for as time served.

Saturday's verdicts prompted international outrage.

A spokesman for the UN high commissioner for human rights, Prince Zeid bin Raad, said: "We are very disturbed by these three sentences and the extra pressure it creates on journalists in Egypt who are just trying to do their jobs."

Allegations against our journalists Judge Hassan Farid: "The court is quite sure that the defendants are not journalists and are not in the journalist syndicate. The defendants have devices for broadcasting without permits, the defendants have made falsified videos, after being edited and aired on a Jazeera screen, and they've aired these videos on a Jazeera channel that isn't allowed to work inside Egypt." Acting AJE Managing Director Giles Trendle:"Firstly, there is no evidence proving that our colleagues in any way fabricated news. This was comprehensively debunked by the court's own technical committee. Secondly, we were not broadcasting in Egypt to Egyptians, therefore we did not require a broadcasting licence. Thirdly, the judge said our colleagues were not journalists. They emphatically are journalists. The court cannot wish away the fact that these three men don't have a longstanding track record and a distinguished body of work. They were journalists and they are journalists."

The European Union said the verdict represented "a setback for freedom of expression in Egypt".

Judge Hassan Farid, in his ruling on Saturday, said he sentenced the men to prison at least partly because they had not registered with the country's journalist "syndicate".

He also said the men brought in equipment without security officials' approval, had broadcast "false news" on Al Jazeera and used a hotel as a broadcasting point without permission.

The verdict was immediately condemned by Mostefa Souag, Al Jazeera Media Network's acting director general, who said: "Today's verdict defies logic and common sense. Our colleagues Baher Mohamed and Mohamed Fahmy will now have to return to prison, and Peter Greste is sentenced in absentia.

World reacts to Al Jazeera journalists' jail sentences

"The whole case has been heavily politicised and has not been conducted in a free and fair manner."

Souag continued: "There is no evidence proving that our colleagues in any way fabricated news or aided and abetted terrorist organisations, and at no point during the long drawn out retrial did any of the unfounded allegations stand up to scrutiny.

"A report issued by a technical committee assigned by the court in Egypt contradicted the accusations made by the public prosecutor and stated in its report that the seized videos were not fabricated.

Shocked. Outraged. Angry. Upset. None of them convey how I feel right now. 3 yr sentences for @bahrooz , @MFFahmy11 and me is so wrong. — Peter Greste (@PeterGreste) August 29, 2015

"Baher, Peter and Mohamed have been sentenced despite the fact that not a shred of evidence was found to support the extraordinary and false charges against them.

"Today's verdict is yet another deliberate attack on press freedom. It is a dark day for the Egyptian judiciary; rather than defend liberties and a free and fair media, they have compromised their independence for political reasons."

Speaking from Sydney, Greste labelled the verdict "outrageous".

"We did nothing wrong. The court presented no evidence. For us to be convicted as terrorists is outrageous. It can only be a political verdict. This is unethical," Greste said.

FAQ: Al Jazeera's journalists on trial in Egypt

Al Jazeera's next step is to file an appeal before the Court of Cassation. Such an appeal should be filed within 60 days.

In January, an appeals court ordered a retrial, saying the initial verdict lacked evidence against the three journalists.

Al Jazeera English's Acting Managing Director Giles Trendle condemns Egypt's sentencings.

Ten previous sessions in the court had all been adjourned.

After Greste was sent back to Australia, Fahmy renounced his Egyptian nationality hoping that he, too, would be deported.

Lynne Yelich, Canadian minister of state for foreign and consular affairs, issued a statement after Saturday's verdict calling on Egyptian authorities to release Fahmy.

"Canada is disappointed with Mohamed Fahmy's conviction today. ‎This decision severely undermines confidence in the rule of law in Egypt," Yelich said.

"The government of Canada continues to call on the Egyptian government to use all tools at its disposal to resolve Mr Fahmy's case and allow his immediate return to Canada."

The three men have received support from governments, media organisations and rights groups from around the world.