In a new report, the organisation denounced the arrest in February 2005 of 13 army officers and warrant officers for the alleged theft of weapons from a military camp south of the capital, Brazzaville.
The body said "army agents", among them one retired official, were being held in Brazzaville prison without trial.
"We do not know the real reason for their arrest because they were never questioned. There was no proper procedure," Roger Bouka-Owoko, the executive director, said.
Some of the inmates, he said, required specialist care for chronic diseases. But, he said, the prisons lacked decent facilities.
The report summarises the investigations into Brazzaville and military prisons by the human-rights NGO.
It said five police officers and civilians, arrested for gunrunning in the southwestern administrative department of Niari, were locked up in Brazzaville prison. The organisation said these people, from 30-40 years old, were arrested in May 2006. They were held in the Specialised Units Headquarters (COMUS), in a western district of Brazzaville, before being transferred to Brazzaville prison on 22 September.
"Their arrest was totally illegal, without an arrest warrant," the rights body said.
It said that since March 2004, three exiled officers from the Democratic Republic of Congo (DRC) had been held without trial in the military intelligence headquarters. They were arrested for political reasons after disturbances in Kinshasa in 2004.
Bouka-Owoko demanded the release of all these prisoners. "When the legal system is unable to judge people within set time limits, they should simply be released. It is a requirement of the rule of law," he said.
However, the public prosecutor of the Brazzaville court (Tribunal de grande instance), Alphonse Dinard Mobangat-Mokondzi, told IRIN on Monday the report contained untruths.
"The charges made by the Congolese human rights organisation are done in bad faith," Mobangat-Mokondzi said.
He said those arrested were not political prisoners, but people who sought to disturb the peace. Of the officers and non-commissioned officers accused of arms smuggling, Mobangat-Mokondzi said: "As regards police custody, the deadline for preventive detention can be prolonged as long as is necessary."
The NGO's report has been sent to government officials - the minister in charge of parliamentary relations, the minister of justice and human rights, the safety, law and order minister - and parliament.
The Brazzaville Public Prosecutor's Office indicated that even officers of the law were accused of arms smuggling.
"That is why the file was sent to the Supreme Court, which has almost completed its review," Mobangat-Mokondzi said.
He said all NGOs, particularly the human-rights body, should collaborate with the Office of the Public Prosecutor because "all of us want human rights to be respected".
However, the bishop of the Church of Awakening, Alain Mpama, said: "In any country, impunity must be fought and, certainly, disorder avoided; but when a citizen is reproached for an unpatriotic act, that person must not be kept in prison for more than a year without a trial. That becomes absurd."
"We sent this report to the International Federation of Human Rights League and to United Nations agencies so that they call the government to account," Bouka-Owoko said.
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