Australian journalist Peter Greste has urged the international community to step up pressure on the Egyptian government to "undo the injustice" meted out to him and two al-Jazeera colleagues, who were sentenced on Saturday to three years in prison by a Cairo court.

Greste, who was deported to Australia in early February, watched the proceedings live in Sydney and said on Sunday he was "absolutely devastated" and "sickened" by the verdict.

His colleagues Mohamed Fahmy, who was married recently, and Baher Mohamed, who has three small children including a boy who turned one on Friday, were taken immediately into custody.

Baher Mohamed received an additional six months' imprisonment and a fine.

The trio were convicted on Saturday of colluding with the banned Muslim Brotherhood, which has been designated as a terrorist organisation, producing news reports that contained "false news" and working as journalists without a press licence.

"This is an injustice. It is absolutely wrong that innocent men should be put into this position," Greste said in Sydney on Sunday.

"The fact is we did nothing wrong. One day in prison would be unjust.

"I know what prison is like, I know what my colleagues are going to have to go back to and what they're going through. Egyptian prisons are never particularly comfortable places at the best of times. I don't know exactly where they're being held at the moment. I'm trying to find that out."

Greste, who now carries the weight of being a convicted terrorist, said the verdict made it "almost impossible for me to continue as a foreign correspondent" because he could not travel to any country that has an extradition treaty with Egypt.

He ran the risk of being arrested and having to fight an extradition order from Egypt, he said, but this was an "inconvenience" compared with what his colleagues were enduring.

He said the trio would "continue to fight this using every available means open to us" and he was grateful for the support of the Australian government and Foreign Affairs Minister Julie Bishop, who had "personally expressed her support and said that she will do everything in her power to use every diplomatic means available also to help".

Ms Bishop said on Saturday she was "dismayed" by the court's decision and would "continue to pursue all diplomatic avenues with my Egyptian counterpart to clear his name".

But Greste said "we need more than just Julie Bishop's support and the Australian government's support" and urged the international community to step up pressure on the Egyptian government.

"We need support from governments around the world, diplomats around the world, indeed for everyone who has ever tweeted or supported or liked Facebook pages or turned up to demonstrations or written letters to continue the fight.

"To give up now, frankly, would be a repudiation of everything they've fought for and everything that we have fought for and will continue to fight for."

Greste said that, in the absence of any evidence of wrongdoing, "the only conclusion we can come to is that this verdict was politically motivated".

"President [Abdel Fattah] el-Sisi now has an opportunity to undo that injustice, to correct that injustice. The eyes of the world are on Egypt.

"It is now up to President el-Sisi to do what he said he would do ... and that is pardon us if we were ever convicted.

"This isn't just about injustice against myself and my two colleagues. This is about what this means for due process in Egypt, it's about what it means for the rule of law in Egypt, it's also about what it means for freedom of the press in Egypt."

The journalists were arrested in Egypt in December 2013, while working for the al-Jazeera network. They were charged with airing false news and aiding the Muslim Brotherhood, a banned organisation in Egypt.

They spent 400 days in jail. In January this year, their convictions were overturned, and, in February, Greste was deported to Australia. Shortly afterward, however, a retrial was ordered and on Saturday the trio were convicted and sentenced.

Greste's legal team, Gilbert + Tobin partner Chris Flynn and barrister Christopher Ward, said in a statement they would continue the fight "inside and outside Egypt".

"As a process, the retrial was a sham and was miscarried at every step," Mr Flynn said.

The Media, Entertainment & Arts Alliance expressed its outrage at the verdict on Sunday and said there was a "very serious prospect that, if these convictions are allowed to stand, the ability of the journalists to be able to travel and to work elsewhere is seriously compromised - an outrageous limitation on their rights given that the charges against them have never been substantiated".

"MEAA, together with freedom of expression and human rights supporters around the world, will continue to campaign for our colleagues," the alliance said.

Human rights lawyer Amal Clooney, who acted for Canadian national Fahmy, said outside court the verdict was not based on evidence.

The verdict "sends a dangerous message that there are judges in Egypt who will allow their courts to become instruments of political repression and propaganda", Ms Clooney said.

The UN Secretary-General Ban Ki-moon said via his spokesman that "he deeply regrets" the court's decision.

"The Secretary-General recalls his earlier appeals for their cases to be resolved expeditiously and in accordance with Egypt's international obligations to protect freedom of expression and association and in full observance of due process guarantees.

"The Secretary-General underscores once again the importance of pluralism and respect for fundamental freedoms for the long-term prosperity and stability of Egypt," his spokesman said.