Authorities in the autonomous region said the five men "had direct relations with a number of foreign entities and the PKK", a Kurdish governmental source told AFP, referring to the Kurdistan Workers' Party, which has led a decades-long insurgency in neighbouring Turkey.

Defence lawyer Aso Hashem told AFP that "three of the five judges of the cassation court upheld the sentence" passed February 16 by a court in Arbil, capital of the region in northern Iraq.

Former judge and lawmaker Latif Moustafa, who left the Kurdish judicial system over its politicisation, confirmed the ruling.

Journalists Ayaz Karam, Kohidar Zebari and Sherwan Sherwani, along with activists Shivan Saed and Harwian Issa, faced multiple charges including "inciting protests and destabilising" Kurdistan, as well as "spying", "armed" struggle and "misuse of electronic devices".

The five men covered or took part in anti-government protests held last year in several Kurdish cities and towns over a major fiscal crisis that caused delayed public sector salaries and pay cuts.

"The nature of these individuals' work had no relationship to journalism or activism but was instead part of a larger plot and sabotage agenda," the governmental source said, adding the Kurdistan Security Council had "released taped confessions".

Human Rights Watch said the charge of "spying" was based in court solely on social media posts and the testimony of "secret informants", who did not appear and were not cross-examined.

"These men were sentenced because of a biased political will," charged Belkis Wille, senior researcher at HRW.

A US State Department report last year on human rights in Kurdistan said "senior leaders reportedly influenced politically sensitive cases".

Sherwani is known for his investigations into corruption and has criticised Kurdish premier Masrour Barzani on Facebook.

The cassation court's decision "represents how significantly Kurdish authorities have allowed free expression to be eroded", Wille added.

The Committee to Protect Journalists in February said the sentence was "unfair and disproportionate" and showed "the Iraqi Kurdistan regional government has finally dropped the pretence of caring about press freedom".

Prime Minister Barzani said in a press conference at the time that the Kurdish government "supports journalism and the rights of journalists in all forms".

On Monday, World Press Freedom Day, journalist Karoukh Othmane was arrested in the Kurdish province of Sulaimaniyah.

Karzan Fadhel, a lawyer and head of the Democracy and Human Rights Development Center in Sulaimaniyah, has listed "74 political prisoners" in Arbil and Dohuk, all "dissidents or protesters indiscriminately arrested on charges of security offences or terrorism".