Congolese politician Jean-Pierre Bemba, his former lawyer and three other allies go on trial at the International Criminal Court on Tuesday charged with corrupting witnesses and interfering with the administration of justice.

Bemba, already on trial at the court for crimes against humanity and war crimes, and his former trial lawyer Aime Kilolo Musamba are accused of coaching witnesses and paying them to testify in his favour between 2011 and 2013.

Last year, prosecutors had to drop their case against Kenyan President Uhuru Kenyatta, accused of fomenting pre-election violence, because of what they said was large-scale intimidation and bribing of witnesses - underlining the difficulties faced by prosecutors at the global war crimes court.

READ: As Uhuru case ends, what’s next for others before ICC?

Jean-Jacques Mangenda Kabongo, another member of Bemba's legal team; Fidele Babala Wandu, a politician and close associate of Bemba; and Narcisse Arido, a witness in Bemba's main trial, face similar charges. All five are citizens of Democratic Republic of Congo.

Bemba and his four co-accused deny the charges and say any payments were intended to cover witnesses' expenses and not to influence their testimony.

Kilolo and the other accused were briefly jailed by the ICC after being arrested by authorities in Belgium, France and Congo, prompting other lawyers defending suspects at the court privately to express concerns at the risks they were running.

Bemba, a former Congo vice-president, has been on trial in The Hague since 2008, accused of orchestrating atrocities against civilians during a 2002 intervention by his Movement for the Liberation of Congo militia in the neighbouring Central African Republic.

Prosecutors cited witness accounts and intercepted phone conversations in which Kilolo discussed giving cash sums in the order of 50 euros to witnesses and concealing the matter from Bemba's other lawyers.

"This isn't corruption," he told one witness, according to prosecutors. "Just a present from Mr. Bemba because you agreed to testify in his favour."

Prosecutors said that on another occasion Kilolo told a colleague, "Our story, our white (colleagues) mustn't hear about this," in apparent reference to Peter Haynes, Bemba's British co-counsel before the ICC.

The five defendants could face sentences of up to five years in prison and an unlimited fine if convicted.