A court in Saudi Arabia has sentenced five people to death for the killing of Washington Post columnist Jamal Khashoggi, who was murdered in the Saudi Consulate in Istanbul last year by a team of Saudi agents.

But Turkey lashed out on Monday at the "scandalous" verdict, saying those responsible for the murder had been granted immunity.

Turkey fuelled international outrage at the 59-year-old Washington Post contributor's death by releasing video footage that contradicted Saudi Arabia's initial denial of involvement.

"Those who dispatched a death squad to Istanbul on a private jet... and sought to sweep this murder under the rug have been granted immunity," President Recep Tayyip Erdogan's top press aide, Fahrettin Altin, wrote on Twitter.

The Saudi court reached a scandalous verdict today after months of secret hearings on the assassination of Jamal Khashoggi. — Fahrettin Altun (@fahrettinaltun) December 23, 2019

Turkish officials said at the time a 15-strong group of killers strangled him and cut his body into pieces. His remains were never found.

Saudi Arabia has said that the killing was carried out by "rogue" elements.

"To claim that a handful of intelligence operatives committed this murder is to mock the world's intelligence," Mr Altin wrote.

"Turkey will continue its efforts to shed light on this incident."

Mr Khashoggi had gone to the Saudi consulate on October 2 last year to obtain paperwork for his wedding to Turkish fiancee Hatice Cengiz.

"I find it unacceptable and far from rules of law," she said, referring to the Saudi sentencing.

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The Turkish foreign ministry said the verdict was "far from meeting the expectations of both our country and the international community to shed light on the murder with all its dimensions and deliver justice".

The ministry also said key aspects of the murder, including the whereabouts of Khashoggi's body, were "left in the dark", which the ministry said was a "fundamental deficiency" in terms of accountability.

"It is not only a legal but also a conscientious responsibility to shed light on this murder committed in our territory and to punish all those responsible," added the ministry.

READ MORE US bars former Saudi diplomat in Turkey from entering US over Khashoggi murder

It reiterated Turkey's expectation of judicial cooperation from Saudi authorities.

Turkey's ties with Saudi Arabia came under strain after the brutal murder, which tarnished the international reputation of Crown Prince Mohammed bin Salman.

Saudi Arabia's state-run Al-Ekhbariya TV channel reported that three others were sentenced to prison. All can appeal the verdicts.

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The crown prince drew international condemnation for the killing because several Saudi agents involved worked directly for him. The kingdom denies that Prince Mohammed bin Salman had any involvement or knowledge of the operation.

State TV also reported the Saudi attorney general's investigation showed that the crown prince's former top adviser, Saud al-Qahtani, had no proven involvement in the killing. Mr al-Qahtani, however, has been sanctioned by the US for his alleged role in the operation.

The trials of the accused were carried out in near total secrecy, though a handful of diplomats, including from Turkey, as well as members of Khashoggi's family were allowed to attend the sessions.

The killing had shocked the world and drawn condemnation from the international community, including the United Nations.

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Agnes Callamard, a UN special rapporteur who authored an inquiry into Khashoggi's killing, later said the search for justice must not be left to the Saudi judicial system, which is "so vulnerable to political interference".

President Donald Trump condemned the killing, and his administration sanctioned 17 Saudis suspected of being involved, though not the crown prince.

Mr Trump, however, has steadfastly resisted calls by members of his own party for a tougher response and has defended maintaining good relations with Saudi Arabia, framing its importance as a major buyer of US military equipment and weapons and saying this creates American jobs.

Meanwhile, numerous critics of the Saudi crown prince remained imprisoned and face trial for their acts of dissent.

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Family welcomes verdict

The son of murdered Saudi journalist Jamal Khashoggi praised the court verdict that saw five people sentenced to death over the killing, saying justice had been served.

"Fairness of the judiciary is based on two principles, justice and swift litigation," Salah Khashoggi, who lives in the kingdom, said on Twitter.

"Today, justice was served to children of... Jamal Khashoggi. We affirm our confidence in the Saudi judiciary at all levels."

إنصاف القضاء يقوم على مبدأين، العدالة وسرعة التقاضي، فلا ظلم ولا مماطلة. اليوم القضاء أنصفنا نحن ابناء المرحوم، بإذن الله جمال خاشقجي. ونؤكد ثقتنا في القضاء السعودي بكافة مستوياته وقيامه بإنصافنا وتحقيق العدالة. الحمد لله والشكر له. — salah khashoggi (@salahkhashoggi) December 23, 2019

Khashoggi - a royal family insider turned critic - was killed and dismembered at the Saudi consulate in Istanbul on October 2, 2018.

The operation involved 15 agents sent from Riyadh, Ankara said. His remains were never found.

Of 11 individuals indicted in the case, five were sentenced to death, three face jail terms totalling 24 years, and the others were acquitted, the public prosecutor said on Monday.

Salah has previously said he had "full confidence" in the judicial system, and criticised opponents he said were seeking to exploit the case.

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The Washington Post reported in April that Khashoggi's children, including Salah, had received multimillion-dollar homes and were being paid thousands of dollars per month by authorities.

But Salah rejected the report, denying discussing a financial settlement with the Saudi government.

Both the CIA and a UN special envoy have directly linked de facto ruler Crown Prince Mohammed bin Salman to the murder, a charge the kingdom denies.