The latest unrest began on Monday after Mozambique’s highest court upheld the victory of Frelim presidential candidate Daniel Chapo in elections held in October.
Mundlein disputed the results, saying the poll was rigged.
In a Facebook live broadcast to his supporters on Tuesday, Mundlein said he rejected the constitutional court ruling, adding that he would take office as president on January 15, the day Chapo is due to be sworn in.
President Filipe Nyusi must resign after two terms.
It is not yet clear how Mondlon is going to take office, as he is currently in self-imposed exile in an unknown country.
He has often rallied his supporters through Facebook Live, but urged them to remain peaceful.
“We are with the people. We do not advocate any form of violence,” Mondlane said in his latest address.
Chapo has not yet commented on his statement.
The October election was the first time they both ran for president, and the electoral commission declared Chapo the winner with 71% of the vote to Mondlon’s 20%.
The Constitutional Court revised the result, giving the Frelimo candidate 65% and Mandlan 24%.
Human rights groups report that more than 100 people have been killed in riots since the election.
They blame security forces for many of the killings, but police chief Bernadino Raphael previously told the BBC that his officers were defending themselves after the attack.
Mundline fled Mozambique after accusing police of threatening behavior and two of his aides were shot dead in October.
The 50-year-old evangelical pastor ran as an independent after breaking away from the main opposition Renamo party.
His support is strongest among young people, many of whom are unemployed and in need of change.
Frelimo nominated 47-year-old Chapo as the youngest presidential candidate.
He previously dismissed suggestions that he and Frelimo had rigged the poll, saying: “We are an organized party that prepares its victories.”
