A lawyer representing a prominent reporter in DR Congo, detained a month ago over an article suggesting intelligence agents assassinated an opposition politician, said Friday that his client was being held illegally.

In a news conference in the capital Kinshasa, lawyer Ndikulu Yana said that his client Stanis Bujakera was being held in prison beyond the court-ordered 15 days, without justification.

Bujakera, who works for Reuters and Jeune Afrique magazine, was detained on September 8 and then transferred to prison on September 15 on suspicion of spreading false information.

His arrest followed a Jeune Afrique article published in late August, which suggested that Congolese military intelligence had killed opposition politician Cherubin Okende the month before.

The article -- which was unsigned -- was based on an alleged confidential memo from a separate intelligence agency. Congolese authorities have said the memo is a fake.

Yana told reporters that the court order to imprison Bujakera for 15 days had long expired.

"Our client is in a situation of irregular detention," he said.

Yana also said that the charges against Bujakera defied basic legal principles, since the journalist was not a signed author of the Jeune Afrique article.

"You can't prosecute someone for the actions of someone else," he said.

The public prosecutor's office identified Bujakera's telephone as the origin of the alleged confidential memo about the killing.

But Yana said the public prosecutor had also stated that Bujakera received the memo via the Telegram messaging app -- contradicting charges that the journalist had been the first to spread the document.

A court in Kinshasa has previously denied requests to release Bujakera on a provisional basis, judging him a flight risk.