Cameroon opposition leader Maurice Kamto, who says he was cheated out of the presidency in elections last year, has been charged with "rebellion" and "insurrection", one of his lawyers said Wednesday.
The former government minister was arrested in the economic capital Douala on January 28 after his MRC party organised protests against October's election result, which they say was rigged.
The prosecutor's office of the Yaounde military court filed the charges against Kamto, his lawyer Emmanuel Simh said. Kamto was transferred to a prison in the capital during the night.
Simh, who is also vice president of Kamto's Movement for the Rebirth of Cameroon (MRC) party, said 28 of Kamto's supporters were also charged.
About 100 other supporters are to appear on Wednesday before the military court, which will decide whether to charge them.
Kamto has said he was the rightful winner of the presidential elections, which were won by the West African country's veteran leader Paul Biya.
Biya, 86, secured a seventh consecutive term with 71 percent of the vote in the polls, which the MRC slammed as an "electoral hold-up".
Kamto won 14 percent of the vote to place second, according to the official figures.
The vote was marred by violence especially in the country's two English-speaking provinces.
Those areas have been badly hit by clashes between separatists and Cameroon troops for more than a year.
MRC supporters protested in several towns and cities on January 26 to dispute the official election result. Police broke up the demonstrations and at least six protesters were injured.
The European Union this month accused Cameroon of a "disproportionate use of force" in dispersing the protests.
"Finding a solution to the challenges faced by the country can only be achieved through dialogue in a calm and inclusive atmosphere where fundamental rights and the rule of law are respected," EU spokeswoman Maja Kocijancic said in a statement.
MRC cancelled other planned protests after Kamto's arrest in a bid to restore calm.
Kamto's lawyers have branded his detention "illegal". They said that authorities had not let him and other detainees receive visitors or help from their lawyers at the special police detention unit in Yaounde.
The MRC has said that around 200 people arrested during the protests are still being held in the capital.
Some of them, including MRC treasurer Alain Fogue, have gone on hunger strike.
Kamto's ex-campaign director Paul-Eric Kingue and rapper Valsero are also detained with him.
Biya has ruled Cameroon since 1982 with support from the army, state administration and the Cameroon People's Democratic Movement (RDPC) that he created in 1985.
Kamto is considered the main opposition to Biya, who turned 86 on Wednesday.
"It's been a long time since Cameroon had an opponent of this stature," analyst Hans de Marie Heungoup at the International Crisis Group said.
"At the start of his career, some called him spineless, but now he really is a relentless political leader," he said.
French foreign ministry spokeswoman Agnes von der Muhll said the government was "worried" by the charges against Kamto.
The Cameroonian opposition "must be able to express itself freely as long as it respects the law," she said in an online news conference.
Human rights groups last month condemned Kamto's arrest and called for his immediate release.
Amnesty International said the arrest of Kamto and his staff "signals an escalating crackdown on opposition leaders, human rights defenders and activists in Cameroon".
"Instead of taking steps towards improving the country's human rights record, we are witnessing the authorities becoming less and less tolerant of criticism. This must stop," said Amnesty's West and Central Africa director Samira Daoud.