Riot policeman aims a tear gas gun in Democratic Republic of Congo's capital Kinshasa, Dec. 10, 2011.

Police in the Democratic Republic of Congo fired tear gas Friday at supporters of opposition leader Etienne Tshisekedi who had gathered for his self-declared "swearing in" ceremony.

Tshisekedi insists he won last month's presidential poll and called on supporters to gather at Martyrs Stadium in the capital, Kinshasa for his inauguration.

The government banned the gathering and dispatched troops, armored vehicles and police throughout the capital, especially to largely pro-Tshisekedi neighborhoods.

Earlier, a Tshisekedi adviser said the ceremony would proceed, despite a government threat to arrest the opposition leader.

The country's electoral commission named incumbent leader Joseph Kabila the winner of last month's presidential election but Tshisekedi, who finished second, rejected the result and proclaimed himself president.

His adviser Valentin Mubake says Kabila won only through "massive fraud" and rejects assertions that Tshisekedi might destabilize the country.

"Before thinking about the destabilization of the country, we have to think about the truth of the vote," said Mubake. "The reality of the elections is that Tshisekedi has been elected by the Congolese people. That [means] the stabilization of Congo and that is reality."

International observers said the poll was deeply flawed, especially in the vote-counting process that American observers termed chaotic.

The election has sparked protests both inside and outside the DRC. On Thursday, rights group Human Rights Watch said Congolese security forces have killed at least 24 people since Kabila's victory was announced last week.

The report said security forces have been firing on small crowds in an apparent attempt to prevent demonstrations.

The Nov. presidential and legislative polls were only the second free elections in the Democratic Republic of Congo's history.

Vote counting in the parliamentary elections was suspended this week. Officials say they need assistance from foreign election experts.