Nairobi, Kenya (CNN) Kenyan opposition leader Raila Odinga, who boycotted the country's disputed election last year, swore himself in as the "people's president" at a mock inauguration ceremony Tuesday in protest against President Uhuru Kenyatta.

Thousands of opposition supporters gathered at Uhuru Park in central Nairobi, chanting slogans and waving tree branches at the symbolic "swearing-in" event, which was organized by Odinga's National Super Alliance (NASA).

The event was largely peaceful, and the throngs of supporters quickly left the park after proceedings had concluded. In what appear to be an isolated incident, police fired tear gas to try to to disperse crowds pulling down signs near the park.

Authorities had earlier said they would put a stop to any illegal meetings, but Reuters reported that no uniformed police could be seen in the park and no anti-riot officers or vehicles were visible.

Afterward, the biography on Odinga's verified Twitter account had been updated to read: "This is the official account of His Excellency Raila Amolo Odinga, President of the Republic of Kenya."

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