By Paul-Marin Ngoupana

OUATA-NANA, Central African Republic (Reuters) - The villagers ran away in panic when rebels brandishing machetes and AK47 assault rifles appeared from the bush, leaving the Red Cross medical workers standing alone in a dusty clearing in Central African Republic.

The landlocked former French colony - one of the poorest places on earth - has been plunged into chaos since the Seleka rebels seized power from President Francois Bozize four months ago, triggering a humanitarian crisis in the heart of Africa largely ignored by the West.

With the country outside the capital Bangui in the grip of rebel warlords, many aid groups and U.N. agencies have pulled out, leaving its 4.5 million inhabitants to fend for themselves.

Rebel Colonel Issene Yaya, who confronted the Red Cross workers in the remote northern village of Ouata-Nata, had come to collect protection money from local chiefs and to lay down the law.

Yaya was furious the Red Cross had not recently visited Ouandago, 10 km (6 miles) from Ouata-Nana, where the rebels had made their base.

"You, Red Cross people...I could make you pay a dear price at the end of my gunbarrel for your behavior," Yaya told the aid workers in the local language Sango. Behind him, his camouflage-clad fighters, wearing protective magical charms, chatted in Arabic, the tongue of neighboring Sudan and eastern Chad.

After delivering an ultimatum to Ouata-Nana's mayor for four local chiefs to bring 800,000 CFA francs ($1,600) to them the next day, the rebels disappeared, leaving the village deserted.

Central African Republic's porous borders mean Arabic-speaking marauding raiders, poachers and soldiers of fortune from neighboring Chad and Sudan form part of the armed groups that have preyed on the countryside in recent years.

Seleka, a coalition of five rebel groups whose name in Sango means 'alliance', launched its uprising after Bozize failed to honor the terms of a previous power sharing deal. Many northerners resented Bozize, who seized power in a 2003 coup, for surrounding himself with his own Gbaya tribesmen.

"What sin, what wickedness did we do for God to reserve this fate for us?" asked Marie Loana, a 72-year-old woman outside her hut in Ouata-Nana, empty after her family fled into the bush.

After the March 24 rebel takeover, Seleka's leader Michel Djotodia was named interim president of Central African Republic in a deal brokered by regional powers intended to lead to elections in 18 months.

But he has failed to prevent his troops, many of whom are Muslims from Chad and Sudan, from committing atrocities against the Christian population.

The International Federation for Human Rights (FIDH) says rebels have killed at least 400 people and carried out dozens of rapes since seizing power. It qualifies this as war crimes.

With health services across the country close to collapse, medical charity Medecins Sans Frontieres has accused the international community of turning its back on the country.

The fighting has displaced 206,000 people inside Central African Republic and pushed 55,000 refugees across its borders.

"We have to appeal to the conscience of the world to help these people living in some of the worst conditions on earth," EU Commissioner for international cooperation Kristalina Georgieva said during a visit this month to the country.

"Unless the state returns, this risks turning into a new Somalia, where local warlords control the country."

"TOTAL IMPUNITY"

In a bid to prevent the nation - which borders with six other states - from dragging the region into anarchy, the African Union last week decided to boost a small regional peacekeeping mission (CEMAC) into a 3,600-strong force.

The decision came after Seleka gunmen killed 15 people in Bangui on July 13 when their truck was found to contain T-shirts supporting Bozize. The bodies of seven victims were found floating in the Ubangi river.

"All seven bodies showed signs of torture. Some of the men had their genitals cut off, their eyes gouged out ... It was really an atrocity," said Joselin Likomba, a Red Cross worker.

Security has improved somewhat inside the chaotic capital this month, following months of looting and killings, after Seleka fighters were ordered off the streets unless patrolling jointly with the CEMAC regional force.

"Seleka fighters are committing crimes with total impunity," FIDH said in a report, estimating the group's ranks had swollen from 5,000 at the time of the coup to some 20,000 fighters.

"In the provinces, where Seleka holds power and the state does not exist, there is no justice."

The European Union, the country's largest humanitarian donor, has so far pledged 20 million euros ($26.5 million) to stabilize the country, hoping this will bring aid groups back.

"The very presence of humanitarian organizations can be a deterrent to looting, killings and rape," said Georgieva, who held long talks with Djotodia in Bangui. "It is not clear he understands how to get a grip on security in his country."

Since independence from France in 1960, Central African Republic has been trapped in a cycle of coup after coup. France's military has intervened more here than anywhere else in Africa, supporting successive military strongmen including self-proclaimed Emperor Jean-Bedel Bokassa from 1966 to 1979.

With President Francois Hollande keen to end France's meddling in its former colonies, French soldiers did not act to stop Seleka toppling Bozize. France's military has secured Bangui airport but otherwise remained neutral.

The humanitarian situation may be about to worsen as terrified villagers flee deep into the forests, scavenging for food, meaning they are missing the planting season. Malnutrition rates, already double those of last year, are poised to leap.

In Ouata-Nana, only one of the village chiefs appeared to pay Yaya 50,000 CFA. Two others fled to Chad while the fourth headed south with his family to Bangui.

"They will kill us if we don't pay," said one of the chiefs, Paul Idamba. "Our life here is torture. It is hell."

($1=496.2410 CFA francs) ($1 = 0.7545 euros)

(Writing by Daniel Flynn; Editing by Pascal Fletcher and Raissa Kasolowsky)