The UN food agency on Wednesday launched one of its largest-ever emergency food airlifts, flying in supplies to the Central African Republic.

The World Food Programme's first cargo aircraft, loaded with 80 tonnes of rice, landed in the capital Bangui in the early afternoon, WFP spokesman Alexis Masciarelli told AFP.

He said there will be 24 daily supply drops to the city, but admitted it was still not enough to meet the desperate need in the conflict-torn country.

"This is a rather exceptional operation, our biggest emergency air operation in a long time, bigger than for Syria and the Philippines," Masciarelli said.

But he added that the operation "would not definitively solve the problem" in CAR, where 1.3 million people -- more than a quarter of the country's population -- is in need of food assistance.

The WFP says a total of 1,800 tonnes of rice will be flown in from Douala in Cameroon, enough for just 150,000 people.

Aid is most desperately needed in camps where more than 800,000 have sought refuge from the sectarian violence that has erupted in the country.

The humanitarian situation in the CAR has deteriorated since a coup in March 2013 led by the mostly Muslim Seleka rebels plunged the country into chaos and led to an outbreak of sectarian attacks between the mostly Muslim ex-rebels and vigilantes from predominantly Christian rural areas.

Amnesty International on Wednesday reported that "ethnic cleansing" was being carried out against Muslim civilians in the majority Christian nation, and that international peacekeepers have been unable to stop it.

Amnesty said it had documented at least 200 killings of Muslim civilians by the mostly Christian anti-balaka ("anti-machete") militia.

"Anti-balaka militias are carrying out violent attacks in an effort to ethnically cleanse Muslims in the Central African Republic," said Joane Mariner, senior crisis response adviser at Amnesty International.

"The result is a Muslim exodus of historic proportions".

French Minister of Defence Jean-Yves Le Drian travelled to Bangui Wednesday to meet with French forces before holding talks with Central African transitional president Catherine Samba Panza.

The previous day in Brazzaville, Le Drian had railed against the militias plaguing the region and said that international forces were prepared to end their abuses "by force if necessary".

"We need all the militias that carry out abuses, that commit murder, to stop," he said.

It marks a shift in tone from France that reflects increasing concern about marauding Christian militias operating with impunity in Bangui and beyond.

On Monday, General Francisco Soriano, commander of Operation Sangaris, described the anti-balaka as "the principal enemies of peace" in the country, who should be treated as "bandits".

The African Union-led MISCA mission has so far failed to end widespread abuses that have led to a mass exodus of Muslim civilians, mainly to neighbouring Chad and Cameroon.

MISCA has around 5,400 troops in the country, while France has deployed 1,600 soldiers under Operation Sangaris.

Amnesty says this is not nearly enough.

"International peacekeeping troops have failed to stop the violence," said senior adviser Donatella Rovera.

"They have acquiesced to violence in some cases by allowing abusive anti-balaka militias to fill the power vacuum created by the Seleka's departure."

The most lethal attack documented by Amnesty took place on January 18 in Bossemptele, where at least 100 Muslims were killed. Women and old men were among the dead, including an imam in his mid-70s.