Amnesty International has said that the trial of Ukrainian citizens Stanislav Klykh and Mykola Karpiuk was "a travesty of justice" and called on Russian authorities to probe the convicts' statements about torture.

"Two Ukrainian men jailed in Russia after being tortured into confessing to a series of murders are the victims of a travesty of justice," Amnesty International said in a statement on Thursday.

Klykh and Karpiuk were convicted of killing Russian soldiers in Chechnya in the 1990s, despite both providing credible evidence that they were not in the unstable region at the time, the statement says.

The Russian Supreme Court upheld sentences of 22 years in jail for Karpiuk and 20 years for Klykh on Wednesday.

"Russia's case against these men defies reason. The numerous fair trial violations and the unconvincing prosecution evidence all point to a fabricated case. They were denied access to their lawyers of choice and allege that their confessions were forced from them as a result of torture," the statement quotes John Dalhuisen, Amnesty International's Europe and Central Asia Regional Office Director, as saying.

"Rather than taking the opportunity to correct this blatant travesty of justice, Moscow's Supreme Court has again overlooked the evidence and upheld the prosecution case in this propaganda-driven show trial," he said.

Klykh and Karpiuk, who belong to a Ukrainian right-wing nationalist group, were unable to use their chosen lawyers for several months after their arrest in 2014, during which time they allege they were tortured into confessing, the statement says.

According to Amnesty International, Klykh said he was forced to drink vodka until he lost consciousness, given mind-altering psychotropic drugs, hung from bars in his cell, subjected to electric shocks and kept in solitary confinement for more than a year. None of these torture allegations have been investigated.

Klykh's state-appointed lawyer was not even present when he was interrogated. It was later revealed that she had been on maternity leave.

"The Russian authorities must investigate the serious allegations of torture at the hands of its law enforcement personnel, as well as the denial of access to a lawyer," Dalhuisen said.

The torture has apparently affected the mental health of Klykh, who appeared severely disturbed throughout the trial, which began in October 2015, the organization said.

"He undressed himself in the court room, shouted abuse and hung himself upside down inside the defendant's cage. In November 2015, Klykh cut himself with a blade to protest against the authorities' refusal to carry out a medical examination. In October 2016, he claimed not to remember his date of birth during a court hearing and asked to be defended by Stanislav Mikhailov – a Russian pop star," the statement reads.

Amnesty International stressed all requests for Klykh to be offered an independent psychiatric examination have been refused and he has instead been declared fit to stand trial. Up to the time of his alleged torture he had no previous history of mental illness.

"To ignore Stanislav Klykh's medical condition, despite the evidence demonstrating his vulnerability, is cruel and inhuman. He must be assessed by an independent medical professional as soon as possible," Dalhuisen said

Karpiuk and Klykh were arrested, while visiting Russia, in March 2014 and August 2014 respectively. They had both been members of the Ukrainian right-wing group, the Ukrainian National Assembly – Ukrainian Peoples' Self Defence (UNA UNSO), which is banned in Russia.

They were convicted by Chechnya's Supreme Court in May 2016 of being members of a group of fighters that killed 30 Russian soldiers during the conflict in Chechnya in 1994-1996.

Both men have denied all the charges, stating that they were in Ukraine at the time of the alleged crimes. Karpyuk was caring for his dying mother who lived in a village near Rivne, Ukraine, while Klykh was a student taking exams.