Baku - Azerbaijan on Thursday released from prison a prominent campaigner sentenced to a lengthy jail term but left his ailing wife, the country's top rights activist, behind bars.Citing the deteriorating health of 60-year-old Arif Yunus, an appeals court judge in the capital Baku ordered him released from custody on the pledge he would not leave the city, an AFP journalist reported from the courtroom. But the court did not address the fate of his 59-year-old wife Leyla Yunus, who is Azerbaijan's top rights campaigner and suffers from a number of ailments including hepatitis C and diabetes.Head of the Institute for Peace and Democracy, one of the tightly-controlled country's leading rights groups, she was jailed in August for eight-and-a-half years on charges that include fraud and tax evasion. Her husband was sentenced to seven years in prison on similar charges. The couple and their supporters have rejected the charges as trumped-up and politically motivated."I was released because of my poor health but Leyla Yunus's health condition is 10 times worse," he told reporters on leaving the courtroom. "She is an ailing old woman," he said, pledging to do everything to secure her release."Even if she is freed right now and sent for treatment to Germany, her health has deteriorated so much that her rehabilitation will take at least three years," he said."She must be set free."His wife had said earlier that she was severely beaten in custody by prison guards. Prisoners of conscienceSpeaking to AFP, her lawyer, Elchin Sadykhov, described her state of health as "alarming" saying he had appealed to the authorities for her release."Arif's release boosts hopes that Leyla may also be freed," prominent women's rights campaigner Novella Jafaroglu told AFP. She expressed hope that Thursday's court decision was the "first step" towards seeing Yunus' wife and dozens of other political activists freed from jail.International rights groups have slammed the prosecution of the Yunus couple as an attempt by Azerbaijan's iron-fisted authorities to prevent them from continuing their work. Amnesty International had earlier demanded an "immediate release" of the couple, describing them as "prisoners of conscience, imprisoned solely for their legitimate human rights work and criticism of the government." Arrested last year on suspicion of spying for arch-foe Armenia, the duo also face treason charges in a separate case. Former KGB officerLeyla Yunus has won several international awards for her work, and has teamed up with Armenian activists to urge reconciliation between the two countries, locked in a decades-long conflict over the disputed Nagorny Karabakh region. Dissent in tightly-controlled Azerbaijan is usually met with a tough government response.Rights groups say the government of the oil-rich ex-Soviet republic has stepped up pressure on opponents since strongman President Ilham Aliyev's re-election for a third term in 2013. Aliyev took over in 2003 after the death of his father Heydar Aliyev, a former KGB officer and communist-era leader who had ruled newly independent Azerbaijan with an iron fist since 1993. Earlier this month, Aliyev's Yeni Azerbaijan party won parliamentary elections, cementing his grip on power.