ABIDJAN (Reuters) - Ivory Coast authorities arrested a senior aide to parliament speaker Guillaume Soro on Monday, a prosecutor said, accusing him of possessing and distributing weapons to destabilize the state during an army mutiny earlier this year.

The arrest of Soro’s protocol chief Souleymane Kamarate Kone and other associates could deepen a rift between the powerful former rebel leader and President Alassane Ouattara.

Renegade soldiers in the second city Bouake used weapons taken from Kone’s home to halt the advance of loyalist troops sent to put down their four-day uprising in May.

Soon after the mutiny, prosecutors opened an investigation into the arms cache, which State Prosecutor Christophe Adou said contained six tonnes of weapons and ammunition.

“The possession and concealment of these weapons in an illegal manner and then their distribution aimed to destabilize the state,” Adou told reporters in the commercial capital Abidjan.

“An inquest with an arrest warrant was opened against him and all persons involved,” he added.

Around 15 people were questioned during the investigation, including Soro’s head of security and his deputy. It was unclear, however, who in addition to Kone was being targeted for arrest.

Kone was taken into custody after questioning on Monday and could not be reached for comment. Allies of Soro say the investigation is politically motivated.

“Kone ... has already served in prison in 2000 for the cause of President Alassane Ouattara. He is a strong man who will remain dignified,” a spokesman for Soro, who is out of the country, wrote in a statement.

The statement also called for supporters to remain calm and for the judicial process to remain independent.

Soro headed a northern rebellion between 2002 and 2011 that helped Ouattara to power after his predecessor Laurent Gbagbo refused to accept defeat in a 2010 election.

However, a split has opened between the president and his former ally this year. Soro is considered one of the main contenders to take over from Ouattara, who cannot run for re-election in 2020, but he faces stiff opposition with the ruling RDR party.

Diplomats and analysts worry that a series of army mutinies beginning in January may be a symptom of jockeying for position by political figures ahead of the 2020 vote.

The arrest of Kone and other Soro associates is likely to increase tensions, including within the army where the parliament speaker still commands the loyalty of many of the thousands of his former fighters now serving as soldiers.