In mid-January, attorney general Githu Muigai filed a High Court petition seeking to block the opposition from swearing in Raila Odinga.
An estimated crowd of 15,000 gathered in a central Nairobi park on Tuesday to cheer Mr Odinga as he took a symbolic presidential oath.
"As an external observer and also a player in the political and security space of East Africa, especially Kenya, I find it quite troubling that the flag-bearer of the opposition NASA party Mr Raila Odinga would have himself sworn in as President even though he withdrew from the election that saw his main contender President Uhuru Kenyatta emerge victor".
Odinga criticized the government's media ban, saying that it confirmed his country has "descended to the level of Uganda", an African nation that had stopped media coverage of elections in 2016.
"It was prudent for the police to keep off a largely peaceful ceremony and prevent a unsafe altercation with opposition supporters", said Manyora.
Njoka said that the criminal designation was based on evidence that the government had seen but did not plan to share, which he alleged may link the group to armed activity in the country.
He said Kalonzo will take the oath later. Image of supporters awaiting Raila Odinga from Reuters. A Kenyan rights group estimated that at least 92 people were killed, mostly by police, in election-related violence previous year.
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On Monday, Linus Kaikai, chairman of the Kenya Editors' Guild, said editors had been warned by authorities that they could be shut down if they covered the event.
According to the management of NTV, Citizen and KTN and Inoro TVs, there has not yet been any official communication as to why this action was taken. The electoral commission has refuted those claims.
Odinga became the first opposition leader to be sworn in as "parallel president" in post-independence Kenya, hence massive anxiety on the outcome of an exercise that was labeled illegal by the government.
The court ordered a fresh election in October that Kenyatta won and Odinga boycotted, claiming a lack of electoral reforms.
Last week, members of Odinga's coalition, the National Super Alliance, released what they said was evidence of vote-rigging showing that Odinga had actually won the August contest.
His explanation, in an audio recording circulated via WhatsApp, could however lead to more confusion around his failure to attend the event as he suggests that he, Musalia Mudavadi and Moses Wetang'ula were blocked from attending.