He added: "Any person acting in violation of Article 3 (2) commits a treasonable offense under Section 40 of the penal code".
Odinga, head of the National Super Alliance, plans to hold a "people's president" inauguration ceremony on Tuesday after President Uhuru Kenyatta took office on November 28 following a bitterly disputed election.
Unless a candidate was declared the victor in an election by the Independent Electoral and Boundaries Commission and the swearing-in was conducted by the Kenyan chief justice, Muigai told a news conference, such a inauguration is "a process wholly unanticipated by the constitution and is null and void".
"The United States also urges Opposition leaders to work within Kenya's laws to pursue the reforms they seek and to avoid extra constitutional actions such as the proposed "inauguration ceremony" on December 12", the U.S. embassy said in a statement. "It is high treason of the persons involved and any other person facilitating that process", he noted.
Odinga's National Super Alliance has said it will proceed with the event.
"The People's Assembly is an institution totally unknown to the constitution of Kenya and totally unknown to the County Governments Act".
Post-Doklam, India, China, Russia to hold trilateral meet
Earlier, Beijing expressed "strong dissatisfaction" with New Delhi on Thursday after "recent crash" of the drone in its territory. The Chinese soldiers soon responded with the location details of the crashed UAV, the ministry went on to say.
Odinga and Kenyatta faced off in an election in August that Kenyatta won.
Raila Odinga alleged Thursday that dozens of Kenyans have been killed by the security forces and "nobody is talking about it. Yet they have the audacity to come and advise us to forget and move on".
Mr Kenyatta was inaugurated last week.
"Our friends can give us advice.in privacy".
Prof Muigai said the government would not stop at anything to prevent the breach of the rule of law and the constitution.