Austrian authorities have voiced their relief after two of the country's residents were released by Iran after years of imprisonment in the country.

Double Austrian-Iranian nationals Kamran Ghaderi and Massud Mossaheb were liberated as part of a prisoner swap involving Europeans and an Iranian diplomat.

The pair's confinement in Iran, on spying and security charges respectively, attracted criticism internationally.

Belgium said a third individual - a Danish resident - had likewise been released.

The trio were flying into Belgium via Oman following medical examinations, Belgian Prime Minister Alexander De Croo said.

Local media reported that they will be met at the Melsbroek military airport just outside Brussels by Foreign Minister Hadja Lahbib.

Her Austrian partner, Alexander Schallenberg, tweeted his relief that the two men could get back home following quite a while of "arduous imprisonment".

In a statement from the foreign ministry, he said Austria would leave "no stone unturned" to secure the release of a third citizen who is still imprisoned in Iran and whose sentence is currently subject to appeal.

Chancellor Karl Nehammer, meanwhile, said the released men's long path of suffering was now at an end.

Mr Ghaderi was arrested in Iran in 2016, and sentenced to ten years in jail on spying charges - after what his family says was a forced confession.

Mr. Mossaheb - who is understood to be in his 70s - was arrested in Teheran in 2019, and sentenced for what Amnesty International has called "vague national security offenses".

The pair spent 2,709 and 1,586 days in confinement respectively.

The earlier prisoner swap between Belgium and Iran involved Belgian aid worker Olivier Vandecasteele and Iranian diplomat Assadollah Assadi.

Mr. Vandecasteele was freed after 455 days in prison, the Belgian prime minister said.

He had been sentenced to 40 years in prison and 74 lashes in January, after being convicted of espionage and several other charges. He denied any wrongdoing.

Mr Assadi was convicted on terrorism charges in Belgium in 2021 in relation to a failed bomb plot in France and had been jailed for 20 years.

Iran's foreign minister said Mr. Assadi had been "illegally detained".

Friday's announcement of the release of the Austrian-Iranian citizens came after mediation talks involving Oman. The Gulf nation also brokered the earlier prisoner exchange.

In his social media post, Mr. Schallenberg called the day "very emotional" after years of discreet diplomatic efforts.

He paid tribute to the Austrian embassy in Tehran as well as his Belgian and Omani counterparts.