NAIROBI, Kenya — Former members of a Muslim militia killed at least 16 people in an attack on a church in the Central African Republic, raising fears that ongoing violence could return to the capital city.

Notre Dame of Fatima, a Roman Catholic church in the capital, Bangui, was attacked Tuesday morning with grenades and gunfire by men allied with a rebel group once known as Seleka, an Islamic faction whose takeover of Bangui five years ago set off the country’s continuing conflict.

Several thousand worshipers were at the church at the time, said Kessy Ekomo-Soignet, a grass-roots activist who runs a youth program in Bangui. The church’s priest, the Rev. Toungoumale Baba, was among the dead. To protest the violence, a large crowd carried Father Baba’s body to the presidential palace, witnesses said.

United Nations peacekeeping officials in Bangui said the attack had followed the arrest of a member of a “criminal group” associated with the former rebel group.