KINSHASA (Reuters) - Tens of thousands of cheering supporters greeted opposition leader Jean-Pierre Bemba on Wednesday as he returned to Democratic Republic of Congo after a decade in prison to submit his candidacy for December’s presidential election.

Bemba, a former vice president and warlord whose war crimes convictions at the International Criminal Court (ICC) in The Hague were quashed on appeal in May, is expected to pose a stiff challenge to President Joseph Kabila or his preferred successor.

After arriving aboard a private jet at Kinshasa airport, Bemba, 55, dressed in a dark suit and a red tie, shook hands with family members and officials from his MLC party before driving off towards the city center in a white SUV.

Throngs of people -- many in T-shirts, hats and scarves bearing his likeness -- lined streets and peered down from pedestrian bridges to catch a glimpse of Bemba, who waved and thrust his fist into the air from the open top of his car.

Police fired teargas near the airport and in the neighborhood of Limite as they tried to clear the road, witnesses said.

Bemba was scheduled to stay at his home in the wealthy riverside Gombe district but was prevented passage “for security reasons”, the police said in a statement. He will instead stay in a hotel, it said.

He is expected to file his candidacy with the electoral commission on Thursday, MLC official Jean-Jacques Mbungani told reporters. He will then fly to his family’s hometown of Gemena in northwestern Congo to pay his respects to his late father.

Slideshow ( 12 images )

“Thank you with all my heart for your encouragement,” Bemba tweeted along with a photo of himself looking out from MLC headquarters over thousands of supporters. “Know that my commitment to restore my country ... remains unchanged.”

His return is expected to energize opposition to Kabila, who has been in power since his father’s assassination in 2001 and is barred by constitutional limits from standing for a new term.

Kabila has refused to commit publicly to not contesting the election. That has kept the country in suspense over whether he will choose someone else to represent his ruling coalition, paving the way for Congo’s first democratic transition, or try to run again and risk a violent backlash.

Security forces have killed dozens of protesters since late 2016 when Kabila refused to step aside at the end of his mandate, saying elections needed more time to be organized. Militia violence in the eastern borderlands has surged since then.

Bemba’s supporters showed little patience on Wednesday. “Kabila, know that Bemba is back,” they chanted.

Slideshow ( 12 images )

ELIGIBLE TO RUN?

The deadline to file candidacies is Aug. 8. Bemba said last week that he believes he is the strongest candidate to represent the opposition but would be willing to make way for another candidate.

His eligibility could be challenged in the courts. The ruling coalition said last week he is disqualified from running by a witness tampering conviction at the ICC, even though convictions for murder, rape and pillage committed by his militia in neighboring Central African Republic in 2002 were thrown out.

Any invalidation of Bemba’s candidacy would infuriate his supporters, especially in western Congo. After his loss to Kabila in the 2006 election, his militiamen and government troops fought gunbattles in the streets of Kinshasa.

“If they try to exclude him, we know that’s political,” said Denise Vila, the provincial coordinator of the MLC’s women’s league. “We are going to fight so that Jean-Pierre Bemba stays in the race.”

Another opposition hopeful, millionaire businessman and former provincial governor Moise Katumbi, plans to return to Congo on Friday after two years in exile but risks arrest due to a conviction for real estate fraud in 2016.

According to a poll released on Tuesday, Katumbi and fellow opposition leader Felix Tshisekedi lead the presidential race with 19 percent support each. Bemba got 17 percent and Kabila nine percent.