US secretary of state John Kerry said it was “chilling and draconian”, British prime minister David Cameron condemned the verdict as “completely appalling” while Australia’s foreign minister, Julie Bishop – whose fellow countryman, Peter Greste, was one of those convicted – said that the “Australian government simply cannot understand it based on the evidence that was presented in the case”.

Australia, the Netherlands and Britain all summoned their respective Egyptian ambassadors to explain the verdict in what marked the fiercest international condemnation of Egypt’s crackdown on dissent since the murder of over 600 anti-government protesters last August.

The backlash followed the sentencing of former BBC correspondent Peter Greste, the ex-CNN journalist Mohamed Fahmy, and local producer Baher Mohamed to seven, seven and 10 years respectively for endangering Egypt’s national security, falsifying news, and helping terrorists. Four students and activists indicted in the case were sentenced to seven years.

Rights campaigners portrayed the verdict as a frightening assault on what remains of Egyptian free speech. But it also represented a shaming slap-down to American diplomacy, coming only a day after John Kerry, America’s top diplomat, landed in Egypt for a brief meeting with Egypt’s president, Abdel-Fattah el-Sisi, in which he raised the impending trial in their discussion and called for Egypt to improve its human rights record. That a guilty verdict was still reached hours later, despite Kerry confirming the return of US military and economic aid to Egypt, represented an embarrassment for US diplomacy, analysts argued.

In court, 10-year sentences were also handed to British journalists Sue Turton and Dominic Kane and the Dutch reporter Rena Netjes, who were not in Egypt but were tried in absentia.

The courtroom, packed with reporters, diplomats and relatives, erupted at the verdict which came despite prosecutors failing “to produce a single shred of solid evidence”, according to Amnesty International, which monitored the trial.

Family and friends of the convicted men broke down in tears, while inside the defendants’ cage the journalists reacted with defiance. Greste, who had only been reporting in Egypt for a fortnight when he was arrested last December, silently held his arm aloft. Fahmy, a dual Canadian-Egyptian national, clung to the bars of the cage as he was pulled away by police, shouting: “They’ll pay for this. I promise you they’ll pay for this.”

Fahmy’s mother and fiancee both broke down in tears, while his brother Adel, who had travelled from his home in Kuwait for the verdict, reacted with fury.

“This is not a system,” he said. “This is not a country. They’ve ruined our lives. It shows everything that’s wrong with the system: it’s corrupt. This country is corrupt through and through.”

Greste’s two younger brothers, Mike and Andrew, who came from Australia to attend court, were grim-faced. “I’m just stunned,” said Andrew Greste, as police pushed reporters from the courtroom. “It’s difficult to comprehend how they can have reached this decision.”

Thousands of miles away in Australia, Greste’s father Juris was filmed receiving the news from his Twitter feed. “That’s crazy, that’s crazy, that’s absolutely crazy,” a distraught Greste senior was heard saying as he walked away from the camera.

Outside the courtroom – as police jostled journalists, and pushed one into the path of a passing car – diplomats and trial observers expressed incredulity at the verdict.

“On the basis of the evidence that we’ve seen, we can’t understand the verdict,” said Ralph King, the Australian ambassador in Cairo.

Evidence provided by the prosecution included footage from channels and events that had nothing to do with Egyptian politics or Al-Jazeera. It included videos of trotting horses filmed by Sky News Arabia, a song by the Australian singer Gotye, and a BBC documentary from Somalia. The prosecution’s case was also severely undermined by the retraction of key testimonies from three lead witnesses, who admitted during proceedings they did not know whether the three journalists had undermined national security – contradicting written claims they made before the trial.

The case was riddled with procedural errors – including the misspelling of the name of convicted Dutch journalist Rena Netjes in the court papers, and her wrong passport number. “It’s ridiculous that a non-existent Dutch citizen with a non-existent passport number has been convicted of terrorism,” Netjes said later by telephone.

Ostensibly, the trial was a broadside against Al-Jazeera, a Qatar-owned news channel that Egypt’s government feels is biased towards Sisi’s predecessor, the Muslim Brotherhood’s Mohamed Mursi. But Mohamed Lotfy, executive director of the Egyptian Commission for Rights and Freedoms, who has observed the trial for Amnesty, said the verdict sent a frightening message to all opposition figures in Egypt.

“It’s a warning to all journalists that they could one day face a similar trial and conviction simply for carrying out their official duties,” Lotfy said. “This feeds into a wider picture of a politicised judiciary and the use of trials to crack down on all opposition voices.”

According to Egypt’s interior ministry, at least 16,000 political prisoners have been arrested since last July’s overthrow of Mohamed Mursi – some of whom have been disappeared, many of whom have been tortured, and many more sentenced to draconian jail terms and death sentences based on little evidence.

In an official Amnesty statement, the group called the verdict a “dark day” for press freedom. “In 12 court sessions,” the statement read, “the prosecution failed to produce a single shred of solid evidence linking the journalists to a terrorism organisation or proving that they had ‘falsified’ news footage.”

Amnesty’s reaction was matched by a furious international response that saw several foreign ministers including Britain’s William Hague expressing outrage at the verdict.

But relatives of the jailed journalists and defendants convicted in absentia said foreign governments must now go beyond banal statements and apply real pressure to help reverse the verdicts. “It’s outrageous that Egypt gets away with this and the rest of the world keeps sending them money,” said Rena Netjes, in views supported by Fahmy’s brother Adel.

“I feel diplomatic pressure is the most important thing,” said Adel Fahmy after leaving court. “There has to be lobbying from any country that cares about the freedom of expression in Egypt. It can’t just be statements any more. They have to make it clear to Egyptians that this is unacceptable.”

But the verdict may have revealed the limits of foreign influence in Egypt, with Egyptian foreign minister Sameh Shoukry issuing a “complete rejection of any foreign interference in the country’s internal affairs.”

It also represented an embarrassing humiliation for John Kerry, analysts argued. The US secretary of state expressed hopes of a positive outcome to the trial in a meeting with Sisi on Sunday – only to find his pleas unanswered the next day.

Commenting on Kerry’s apparent ineffectiveness, Michael Hanna, Egypt analyst at the Century Foundation, said: “When you’re thinking of making a stop in Egypt, there are a whole range of issues that come into play. And one of the things you have to consider is the pending verdict. The trip could have made sense if assurances had been given regarding the verdict. But if not, then it’s sloppy scheduling.”

Inside Egypt, where Al-Jazeera journalists are portrayed as terrorists due to their perceived support for the ousted Mursi, many cheered the verdict. “Aljazeera channel are evil,” wrote one Twitter user in a typical response. “They support only the [Muslim Brotherhood] and change stories and want to show Egypt [is] not safe for tourism.”

It is this hostile domestic reaction to Al-Jazeera that may dissuade Egypt’s new president from pardoning the defendants – a move foreign observers have optimistically speculated Sisi might now take. In the absence of a pardon, the convicted journalists will have to navigate Egypt’s appeals system – a process that is considered less politicised than the rest of Egypt’s judiciary, but may take until at least October to start. “We’ve lost a good amount of faith in the justice system,” said Greste’s brother Mike after Monday’s verdict. “But [an appeal] may be the only process left available to us.