Five pro-democracy campaigners held without trial in the Democratic Republic of Congo since December were to go before a prosecutor Thursday, their lawyer said as human rights groups pressed their case.

"The five activists from the Filimbi movement -- Carbone Beni, Mino Bopomi, Cedric Kalonji, Grace Tshunza and Palmer Kabeya -- were transferred yesterday to the high court prosecutor in Gombe," a wealthy part of the capital, defence lawyer Chris-Sam Kabeya told AFP.

Kebeya said the five "will be presented today before a prosecutor who will determine their fate".

The activists were arrested as they mobilised residents of the capital Kinshasa for a nationwide rally on December 31 last year against the extended rule of President Joseph Kabila. Six people were killed during the protests and the crackdown sparked international condemnation.

Human rights groups and the five's families have protested their detention ever since, alleging they were held arbitrarily in ANR intelligence service dungeons and subjected to torture.

The families last Friday demanded they either be released or be brought before a prosecutor while MONUSCO, the UN mission in DRC, said it was closely monitoring developments.

On that occasion, another lawyer for the group said that Beni, their leader, whose release Human Rights Watch urged a month ago, had stomach and knee problems and had undergone surgery, while Kabeya and Kalonji were also "in a very bad state" but had not received any health care.

'Promises of death'

A former civil servant, now an activist with a women's movement in the eastern town of Goma, was reported transferred to ANR headquarters in Kinshasa last month while, nationwide "around 100 people" are being held in secret, says the Congolese Association for Access to Justice (ACAJ), a figure MONUSCO cannot itself confirm.

"Filimbi activists are among hundreds of pro-democracy activists and human rights defenders, journalists and opposition supporters arrested since 2015," says Human Rights Watch, adding many have been held without charge or access to family or lawyers.

HRW and ACAJ stress that under DRC law, detainees are entitled to access to a lawyer within 48 hours.

Fred Bauma, a Lucha citizen movement activist held for 17 months who spent time in ANR detention, told Jeune Afrique magazine in 2016 he faced "daily threats from hundreds of ANR agents (who) repeatedly promised us death."

Another activist told AFP of "highly degrading and inhuman" conditions akin to "creeping death" with ten-strong groups packed into grimy cells where they slept on the floor and received one meal a day.

A high ranking military intelligence official insisted to AFP that "there are no civilians in detention."