Tchiroma, who challenged President Paul Biya's 43-year grip on power in the October 12th ballot, had called on his supporters to hold peaceful marches.
Deadly protests have been held to challenge the election held in Cameroon.
This is as 92-year-old Paul Biya is set to begin another 7-year tenure after being declared winner of the presidential election.
He has been ruling the country for 43 years.
However, four people were killed in clashes between security forces and supporters of opposition leader Issa Tchiroma.
Tchiroma, who challenged President Paul Biya's 43-year grip on power in the October 12th ballot, had called on his supporters to hold peaceful marches on the eve of the announcement, despite a national ban on public gatherings.
The opposition figure claims to have won 54.8 percent of the vote, against the 31.3 percent he attributes to the 92-year-old incumbent, Paul Biya.
In Douala, Cameroon’s largest city, the regional governor reported that on Sunday, demonstrators “attacked” police stations and a gendarmerie brigade in two districts.
The governor confirmed the tragic toll: “Four people unfortunately lost their lives,” and added that several members of the security forces were also injured.