The motley crew of fighters who overthrew the Central African Republic's government in March are raging beyond their leader's control, terrorising civilians and pushing the country toward civil war, analysts say.

The Seleka rebels -- a loose band of veteran insurgents who picked up mercenaries, robbers and an assortment of other violent men on the way -- have continued their rampage despite being officially dissolved by the man they installed as president, Michel Djotodia.

What started as a movement to oust then-president Francois Bozize has gone off-script, the mostly Muslim Seleka fighters burning and pillaging villages, the majority Christian population responding with their own militias that have themselves killed innocent Muslims in reprisal.

"These armed groups are taking advantage of the situation to carry out raids and massacres. Villages are being burnt and looted. The residents are either killed or flee to the bush," said Jean-Marie Fardeau, director of Human Rights Watch's French office.

France, the Central African Republic's former colonial ruler, said Tuesday it would send about 1,000 soldiers to bolster its current mission of 410 troops and help a struggling African mission to stabilise the country.

France has also proposed a United Nations Security Council resolution authorising international troops to use force to stop ongoing atrocities.

The rebels' transformation into common criminals has been increasingly visible in recent weeks in the capital, Bangui. Victims speak of men committing horribly violent rapes, stealing a moped by throwing a grenade in the street, robbing a market-woman in a spray of machine-gun fire.

As they advanced on Bangui, the rebels picked up mercenaries from neighbouring Chad and Sudan, professional highway robbers and thousands of young men who joined their cause in the final hours.

Djotodia's failure to restore full state control has given violent, often drunk or high ex-rebels free rein to wreak havoc in a country already troubled by a long history of coups, conflict and instability.

Reports of civilian massacres with religious overtones last week prompted the UN, France and the United States to warn the country was on the verge of a genocide.

Officials have since backed off that word, which experts say doesn't quite fit the disorganised chaos in the Central African Republic -- at least not yet -- and which arguably requires countries to intervene under the UN genocide convention, something world powers have shown reluctance to do in the past.

"One can speak of a 'criminal strategy' among the armed groups, but there's no coordination, nor planning among them," said Fardeau. "The term 'genocide' is not apt."

Aside from a history of clashes between nomadic Muslim herders and sedentary Christian farmers, religious conflict had never been an issue in the Central African Republic, where Muslims have long lived side-by-side with the Christian majority.

"The crisis isn't religious, it's above all an economic and political crisis," said Nestor Desire Nongo Aziagbia, the Catholic bishop of the town of Bossangoa, which has been at the heart of the communal violence.

The conflict has only increased the suffering of one of the world's poorest countries, where life expectancy is 49 years old, the average adult has three and a half years of schooling and the average income is less than $2 a day.

The UN estimates at least 400,000 people, or 10 percent of the population, have been forced from their homes.

French researcher Roland Marchal said innocent civilians are the worst affected.

"The primary Christian victims are villagers who never asked for anything, and the Muslim victims are often traders or nomads who have nothing to do with Seleka," he said.