* 30 houses burn overnight in northern Bangui
* French, African troops fail to stop killings
* MSF charity says adolescent, baby among recent dead (Adds President Djotodia comment, reaction from Congo)
By Serge Leger Kokpakpa and Paul-Marin Ngoupana
BANGUI, Jan 1 (Reuters) - Clashes between Muslims and Christians in Central African Republic's capital killed at least three on Wednesday as angry residents threw grenades and torched homes, witnesses said.
French and African troops deployed in the country have struggled to stop the tit-for-tat violence between Muslim Seleka rebels, who seized power in March, and Christian self-defence militia, clashes that killed more than 1,000 people in December.
Residents of Bangui said that Seleka forces wearing civilian clothes threw grenades at Christian houses in a northern district of the city, setting them alight. Christian youths then launched reprisal attacks, burning nearby Muslim homes.
"The Muslims came and set fire to the houses ... everyone was affected," said Aristide Yenga, resident of the Ngou Simon neighbourhood in the north of the capital Bangui.
"This morning they began shooting and when we heard that we left for the larger (displaced persons') camps."
The body of a Seleka fighter with his left hand severed off and missing lay in the middle of a large dirt avenue following the attacks, a Reuters witness said. A resident of the neighbourhood who asked not to be named said that two other Muslims had been killed there overnight.
No peacekeepers were present, although a French helicopter flew overhead, the Reuters witness said.
The incidents occurred in the city's fifth district which houses both Muslims and Christians and near where heavy artillery battles took place the previous two nights.
Despite the ongoing violence, interim President Michel Djotodia called on those that have fled their homes to return in a New Year's speech on Wednesday.
Meanwhile, the President of neighbouring Republic of Congo Denis Sassou-Nguesso warned of the "tragic and fatal" consequences of CAR's implosion for the region.
"It is imperative that we avoid such a disastrous outcome," he said in a speech on Wednesday.
A doctor at medical charity MSF at a makeshift camp at Bangui airport housing over 100,000 displaced people said on Wednesday it had received around 15 injured and two dead.
"Among the two dead was an adolescent of 12 years with a gash on his skull," said MSF's Gaetan Adouaka.
It was not clear if those killed were the Muslims from the northern district. The previous day a four-month-old baby died from a gunshot wound, the charity said in an earlier statement.
Aid workers say they are struggling to provide for the country's more than 800,000 displaced people, most of whom are now living in crowded camps, because ongoing violence is disrupting supplies.
Others have fled via boats across the Congo River or on emergency flights to nearby countries.
Central African Republic is one of Africa's poorest states despite abundant mineral resources. It is also one of the least stable and has seen five coups and several rebellions since independence from France in 1960. (Writing by Emma Farge in Dakar; Editing by John Stonestreet and Chris Reese)