A former vice president of the Democratic Republic of Congo pleaded not guilty Tuesday to charges of interfering with the administration of justice by coaching and paying defense witnesses to give false testimony in his war crimes trial.

Jean-Pierre Bemba was among five defendants who went on trial at the International Criminal Court charged in an alleged plot to deceive judges in Bemba's prosecution on charges including murder, rape and pillage allegedly carried out by his militia in Central African Republic from 2002-2003.

All five pleaded not guilty as the trial got underway. They face a maximum sentence of five years imprisonment and a fine if convicted.

Manipulating witnesses, either through intimidation or bribery, is a major concern of the world's first permanent tribunal prosecuting war crimes and crimes against humanity. It has been a recurring problem in cases focusing on post-election violence in Kenya.

Prosecutors said the trial that started Tuesday is a crucial step in safeguarding the court's integrity.

"The principles of fairness and justice for which this institution was established have to be protected," said the court's chief prosecutor, Fatou Bensouda.

Prosecution senior trial lawyer Kweku Vanderpuye told judges that the defendants had a detailed plan to coach defense witnesses in Bemba's Central African Republic trial, which ended nearly a year ago. Judges have not yet delivered their verdicts in that case.

Vanderpuye said that Bemba, his lawyer, Aime Kilolo, and case manager Jean-Jacques Mangenda — who is a former ICC staff member — "corruptly influenced the testimony of numerous defense witnesses." Also standing trial were Bemba's political ally, Fidele Babala, and Narcisse Arido, who allegedly scripted some defense witness testimony.

They used code words and illicit mobile phones to discuss and attempt to hide their plot, Vanderpuye said. "Cafe" was code for money and "couleur" was used to refer to illicit coaching of witnesses by Bemba's defense team, he told judges.