* Christian militia attacks convoy of Muslims being evacuated
* Fighting rages near Bangui airport
* U.N. aid official forced to cancel visit to north of country (Adds Chad PM, Seleka commander comments, details)
By Media Coulibaly
BANGUI, Feb 19 (Reuters) - Heavy fighting erupted near the airport in Central African Republic's capital Bangui on Wednesday, as Christian militia tried to block the evacuation of Muslims and disrupted a visit by a top United Nations aid official, witnesses said.
The fighting was the latest episode in a cycle of religious violence that has displaced an estimated 1 million people from the former French colony and killed at least 2,000.
About 6,000 African and 1,600 French peacekeepers have failed to halt the conflict. Paris has warned the crisis risks degenerating into genocide.
The latest clashes began after Chadian troops tried to escort a convoy of Muslims out of the city, said Songokoua Yetinzapa, a Bangui resident living in a vast camp for displaced civilians near the airport. Their departure was blocked by the militia, known as the "anti-balaka," which means "anti-machete" in the Sango language.
"I heard several people were killed, but I only saw one dead body: a Muslim who was killed by the anti-balaka," he said by telephone as automatic gunfire and an explosion rang out.
Reuters journalists were chased from the scene by machete-wielding youths.
Sebastien Wenezoui, a spokesman for the anti-balaka, said their fighters came out to defend the local population near the airport after they were targeted by Chadian troops who were escorting the convoy.
"When they drove in from Chad yesterday, the Chadians attacked civilians in Damara. Someone from the town called a radio program to report what the Chadians did. This angered people in Bangui who set up roadblocks to prevent them from leaving," Wenezoui told Reuters by telephone.
He also said African MISCA peacekeeping troops and French soldiers removed the roadblocks and dispersed the crowds. Some anti-balaka fighters responded with gunfire.
Chadian troops then "passed forcefully" through the barricades, a foreign military source said, asking not to be named. French army spokesman Gilles Jaron said that there was sporadic gunfire in the direction of French troops, but gave no further details.
A U.N. official confirmed African peacekeepers had been dispatched to reinforce troops in the area near the airport.
"IMPOSSIBLE TO JUSTIFY"
Another U.N. official said the fighting had prevented Valerie Amos, U.N. Under-Secretary-General for Humanitarian Affairs, from traveling to the north of the country, where violence between Muslims and Christians has also scattered tens of thousands of civilians and left villages abandoned.
Predominately Muslim rebels, known as Seleka, toppled the president of the Central African Republic, Francois Bozize, last March. Killings and abuses carried out while they were in power led to the creation of a mainly Christian self-defense militia known as "anti-balaka."
Violence targeting Muslim civilians has increased since Seleka leader Michel Djotodia resigned as president last month under international pressure.
International forces including elite units of the Chadian military and African peacekeepers have evacuated tens of thousands of Muslims from areas under the control of anti-balaka forces in the absence of government troops.
Chad has so far repatriated more than 70,000 of its nationals from Central African Republic since the end of December as part of an operation that Chadian Prime Minister Kalzeubet Pahimi Deubet said had now ended.
Speaking on Chadian state television, Deubet said Wednesday's violence targeted a convoy containing Chadian civilians and came a day after a similar attack 50 km (31 miles) from Bangui.
"Repeated attacks on convoys carrying defenseless people committed through the barbarity of those whom they considered their brothers is impossible to justify," he said.
A retreat of most Seleka forces from Bangui following Djotodia's resignation has led to Muslims fleeing the south and warnings from a top U.N. official of "ethnic-religious cleansing."
While some Seleka officials have mooted the possibility of a partition of the country, General Moussa Dhaffane, a senior rebel commander who has remained in Bangui, called upon Muslims to return.
"We must ask those who left, Central African Muslims, to return. This is their home. This is their land, their soil. Their homes are here," he told a press conference on Wednesday. (Additional reporting by Bate Felix and David Lewis in Dakar; writing by David Lewis and Joe Bavier; editing by Daniel Flynn, Larry King and G Crosse)