ABIDJAN (Reuters) - A United Nations experts mission is assisting Ivory Coast authorities investigating an arms cache discovered last month in the home of an aide to parliament speaker Guillaume Soro, a government spokesman said on Thursday.

Dozens of crates of weapons and ammunition were seized from a house in the second-biggest city, Bouake, owned by Soro ally Souleymane Kamarate Kone - known locally as ‘Soul to Soul’ - by mutinous soldiers during a four-day revolt over bonus payments.

The mutineers had been running out of ammunition and the arms cache helped shift momentum in their favor, forcing the government to capitulate to their demands.

The discovery of the weapons at the home of Kone - Soro’s director of protocol - has provoked public speculation of links between the speaker and the mutiny.

The government’s request for U.N. assistance is the latest indication that Ivorian authorities are carrying out a serious investigation into the affair.

Kone along with two senior military officers serving as aides to Soro have already been questioned by gendarmes and a prosecutor. Soro - a main contender to take over from President Alassane Ouattara, who cannot run for re-election in 2020 - has declined to speak publicly about the weapons.

“The dossier is with the prosecutor. The government felt there was a need for expertise and it made a request,” Communications Minister Bruno Kone said, confirming the participation of U.N. personnel in the investigation.

He declined to give further details. A spokeswoman with Ivory Coast’s U.N. peacekeeping mission, which is in the process of winding down after more than a decade, said she was not aware of U.N involvement in the investigation.

The image of Ivory Coast - the world’s top cocoa grower and Africa’s fastest growing economy - as a post-war success story has suffered a blow this year amid a wave of mutinies that have exposed the government’s tenuous control over the military.

Soro headed the New Forces rebellion that occupied northern Ivory Coast from 2002 to 2011 and helped Ouattara to power during a civil war sparked by his predecessor Laurent Gbagbo’s refusal to accept defeat in a 2010 run-off election.

Soro’s presumed aspirations to the presidency have provoked strong opposition from others in the ruling coalition.

Last month’s mutineers were former New Forces rebels who had been integrated into the army. The military is now seeking to recuperate the weapons, which included assault rifles, machineguns and rocket-propelled grenades along with ammunition.