International NGOs accuse the regime of President Paul Biya, who has ruled with an iron fist for more than 41 years, of systematically suppressing opposition.
"The Political Alliance for Change (APC) and the Alliance for Political Transition in Cameroon (ATP) are not political parties under the law," said Territorial Administration Minister Paul Atanga Nji in a statement late Tuesday.
"These clandestine movements cannot carry out any political activity.
"Despite the illegal character of these movements, their promoters hold meetings, press conferences and consultations looking to recruit new members," he said.
The statement also expressed concern over "pseudo-associations ahead of the 2025 presidential election."
The APC dismissed what it called "curious threats," in a "statement which indicates panic."
The alliance said it was "ready to face the elections victoriously" next year.
The APC, led by former deputy Jean Michel Nintcheu, was set up in December at a congress of the leading opposition Movement for the Renaissance of Cameroon (MRC), which backed Maurice Kamto for president in the 2018 ballot.
Kamto came second and called Biya's re-election a fraud. He was jailed without trial the following year, after staging peaceful protests.
The movement boycotted legislative elections in 2018 and over the next two years saw 700 of its supporters imprisoned, including Kamto.
Most were freed after eight months in detention without trial but 47 were jailed by a military tribunal in 2021 — 44 remain in prison today.
Rights group Amnesty international last year charged 91-year-old Biya's regime with using military tribunals to arbitrarily detain the opposition, civilians, journalists and civil society figures on the pretext that they had committed terrorist acts.
Forum