An international court is expected to approve the early release from prison of one of the architects of the 1994 genocide in Rwanda – despite objections from prosecutors who claim it will undermine confidence in global campaigns to combat extremism.

The Rwandan government has also made protests over what it describes as a secretive process which could see Hassan Ngeze freed along with others responsible for the slaughter of 800,000 Tutsis.

It is demanding a public hearing so objections from survivors of the genocide can be heard. Ngeze was the editor of a newspaper, Kangura, which routinely dehumanised and incited violence against Tutsis, and was a founder of an extremist Hutu political party whose leaders presided over the mass killings.

Ngeze called for the murder of Tutsis, armed the killers and selected individuals to die. He was convicted by the international criminal tribunal for Rwanda (ICTR) on several counts of genocide-related crimes, and of aiding and abetting extermination as a crime against humanity.

The conviction was upheld by an appeal court which said: “Ngeze used the publication (Kangura) to instil hatred, promote fear, and incite genocide.”

Now, after completing two-thirds of a 35-year sentence, Ngeze has applied for early release. Lawyers expect that it will be granted later this month by Theodor Meron, an American who heads the international court which took over responsibility for administering sentences after the individual tribunals for Rwanda and Yugoslavia were wound up.

Rwandan officials have strongly criticised Meron for granting reductions in sentences and early release for a number of people convicted of genocide.

The government in Kigali said there is nothing in the ICTR statute which requires release of prisoners after completing two-thirds of their sentences and that the measure is a “judicially-invented creation” imposed without consulting Rwanda.

The policy also raises the prospect that the chief architect of the attempted extermination the Tutsi population, Théoneste Bagosora, could be released later this year in a move that would anger not only Rwanda but also the Belgian government because of the former army colonel’s role in the murder of 10 of its UN peacekeepers.

Simone Monasebian, one of the international prosecutors at the trial of Ngeze and others involved in anti-Tutsi propaganda, has written to Meron describing him as a “mastermind of the genocide” and objecting to his release.

The accused “were duly convicted of crimes that shocked the conscience of humanity,” she said in the letter. “Their newspaper and radio station fuelled the genocide and were more potent and dangerous than any bullets or machetes.”

Ngeze was responsible for the publication of the Hutu Ten Commandments which said Hutu men were traitors if they married or befriended Tutsi women, that Tutsis are “dishonest in business” and only interested in “the supremacy of their ethnic group”, and that only Hutus should be in positions of power or administrative control.

“The Hutu should stop having mercy on the Tutsi,” it said.

Monasebian, who is now director of the UN Office on Drugs and Crime in New York, said that Ngeze and his fellow defendants have yet to show remorse for their role in the killings.

Rwandans place the skulls of several hundred Tutsi civilians into bags after a memorial for approximately 12,000 Tutsi massacred by Hutu militia in and around the western town of Kaduha. Photograph: Reuters

“To this day, they refuse to recognise it was a genocide against the Tutsi. To this day, they refuse to accept any responsibility for their actions. They are unrepentant violent extremists,” she said.

Another prosecutor in the case described the prospect of Ngeze’s early release as “appalling” at a time when the UN and international community are trying to counter violent extremism.

“What sort of message will be passed to not only the genocide victims but the world at large when a person who was considered a violent extremist and was also instrumental in setting Rwanda afire in 1994 is set free while the damage of his extremist actions continues to be felt?” wrote Charity Kagwi-Ndungu in a letter to Meron’s court.

Ngeze’s release is being considered alongside that of two other men convicted of genocide.

Aloys Simba is a former lieutenant colonel who organised large-scale killings in the south of the country.

Dominique Ntawukuriryayo was a local official who lured Tutsis to their deaths with promises of protection and then handed them over to the Hutu Interahamwe militia to be murdered.

Rwanda’s justice minister and attorney general, Johnston Busingye, has written to Meron objecting to any of the three being freed at this time.

“Their release from prison would cause untold psychological harm for the survivors of the genocide against the Tutsi, and it would contribute to the erosion of the international criminal justice system,” he said.

“Not since the routinised slaughter of the Jewish people during the Holocaust had the world witnessed such a systematised effort to exterminate a people. The severity and gravity of these crimes should be sufficient, without more, to deny these prisoners’ applications for early release.”