* Ban Ki-moon evokes spectre of Rwandan genocide on visit to CAR
* Chad starts withdrawing troops after criticism
* C.African Republic asks for end to U.N. arms embargo (Edits, adds comment from Chad, CAR government)
By Hubert-Mary Djamany
BANGUI, April 5 (Reuters) - French and African soldiers serving in Central African Republic are "overwhelmed" by the "state of anarchy" in the country, U.N. Secretary-General Ban Ki-moon said on Saturday, a day after Chadian troops began withdrawing from the peacekeeping mission.
The U.N. Security Council is due to approve next week a 12,000-strong U.N. peacekeeping force for the former French colony. The force will take over authority from African Union troops in an attempt to restore order to the country.
But that force is not expected to arrive until September, stoking fears of a security vacuum as the interim government struggles to control intercommunal violence that has killed more than 2,000 people since December.
During a brief visit to the impoverished country on his way to Rwanda, Ban appealed for more help and said the international community was at risk of repeating the mistakes of the 1994 Rwanda genocide, where some 800,000 died.
"I commend the African Union and French forces for making a difference," he said in a speech before the interim government. "But they are under-resourced and overwhelmed by the sheer scale of the need."
Until the U.N. force can be established, Ban called for "the immediate deployment of more troops and police", though he did not say where he thought the extra forces might come from.
A long-promised European Union force is expected to start deploying at the end of this month, adding 800 new troops.
"The international community failed the people of Rwanda 20 years ago. And we are at risk of not doing enough for the people of the CAR today," Ban said.
At the same gathering, the head of the interim government, Alexandre-Ferdinand Nguendet, requested an end to a U.N. embargo on arms exports to his country. "That way, the army can play its role," he said.
Two thousand French peacekeepers and 6,000 African Union forces have failed to stop a conflict that erupted after the mostly Muslim Seleka rebels seized power a year ago in the majority Christian state.
Christian militias, known as anti-balaka, sprang up to protect the population after Seleka took to looting and killing but now stand accused of human rights abuses themselves and last month were branded as "terrorists" by the African Union.
Highlighting the tensions in Bangui, gunshots were heard around noon on Saturday coming from the Seleka barracks, a Reuters witness said. Earlier in the day, Seleka members stabbed a member of the national army, a resident said. It was not clear whether the victim survived.
Chad, which has been at the heart of the peacekeeping mission, began withdrawing around 850 troops on Friday after allegations they were involved in attacks on civilians.
A U.N. report on Friday accused Chad of killing 30 civilians and wounding 300 in a crowded market, although Chad denied the allegation, saying its troops were ambushed by anti-balaka.
"The U.N. report is a pack of lies based on imaginary facts. It contributes to the media campaign against Chad," said government spokesman Hassan Sylla on Saturday.
The U.S. ambassador to the United Nations, Samantha Power, plans to visit Central African Republic next week. (Additional reporting by Michelle Nichols in New York; Writing by Emma Farge; Editing by Prudence Crowther and Gareth Jones)