Former warlord and ex-vice president Jean-Pierre Bemba returned to the Democratic Republic of Congo on Wednesday after an 11-year absence, an AFP reporter saw.
Bemba, 55, arriving at Kinshasa airport from Belgium aboard a private plane, has vowed to contest the country's twice-delayed elections, due on December 23.
A few minutes after landing, Bemba, accompanied by his wife, went into a VIP suite at the airport.
Hundreds of police clad in anti-riot gear were deployed in central Kinshasa and at the airport, located 25km from the city.
In June, Bemba was acquitted of war-crimes charges by the International Criminal Court (ICC) in The Hague after spending a decade behind bars.
Analysts say his return adds volatility to an already tense election for which candidates must submit their applications by August 8.
The DRC has never known a peaceful transition of power since it gained independence in 1960 - and some experts fear that the December elections may trigger a bloody conflict.
Kabila, 47, has been at the helm since 2001, presiding over a vast mineral-rich country with a reputation for corruption, inequality and unrest.
He was scheduled to stand down at the end of 2016 after his second elected term, technically the last permitted under the constitution.
But he has stayed in office, invoking a constitutional clause enabling him to stay in power until a successor is elected.
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