Guillaume Soro, a former rebel leader in Côte d'Ivoire and a candidate in next year's presidential election, could face life in prison over an alleged coup plot that involved amassing weapons, the country's public prosecutor said on Thursday.

The Ivorian authorities issued an arrest warrant for Soro on Monday, prompting him to call off a planned homecoming after months overseas.

The warrant is likely to increase tensions ahead of an October 2020 election that is seen as a test of Côte d'Ivoire's stability after two civil wars since the turn of the century.

During a news conference, Prosecutor Richard Adou played a recording made by the Ivorian intelligence services in which Soro could allegedly be heard planning a coup.

"The penalty for attempting a plot against state security is a life sentence," Adou said, adding that the investigation was ongoing.

Soro's lawyer and spokeswoman Affoussy Bamba Lamine did not deny the authenticity of the recording presented by prosecutors but said it was from 2017 and incomplete. She said in a video posted on Facebook on Thursday that Soro's team would release a full version of the audio soon.

Soro is believed to be in Europe although his exact whereabouts are unclear. He has denounced the case against him as being politically motivated.

"It is only in a dictatorship that an arrest warrant is issued against an electoral candidate," he said on Twitter on Wednesday.

So far, more than 15 people have been arrested in connection with the investigation, which includes charges of money-laundering and amassing illegal weapons, the prosecutor said.

"Searches of homes of the accused parties, including Soro, uncovered arms such as anti-tank missiles, RPGs (rocket-propelled grenades), Kalashnikovs, and ammunition.”

Soro, 47, led the rebels who failed to oust then-president Laurent Gbagbo in 2002. Soro's forces installed President Alassane Ouattara during a civil war that followed the 2010 election, in which both Gbagbo and Ouattara claimed victory.

Ouattara won re-election in 2015 but has given mixed signals about whether he will seek a third term, adding to uncertainty about the vote in Francophone West Africa's largest economy.

Soro retains the loyalty of many former rebel commanders who hold senior positions in the army. He served for several years as speaker of the National Assembly but has since fallen out with Ouattara.