Armed groups in the Central African Republic (CAR) have killed at least 45 civilians in apparent reprisal strikes over the past three months, a human-rights watchdog says in a new report.

The violence pitted armed groups against one another in the central province of Ouaka, which is on the border of the mainly Muslim north and the mainly Christian south of the country.

"As factions vie for power in the Central African Republic, civilians on all sides are exposed to their deadly attacks," Lewis Mudge, Africa researcher at the US-based Human Rights Watch (HRW), said on Tuesday.

CAR has seen violence since 2013, when a mainly Muslim rebel coalition called the Seleka toppled President Francois Bozize and went on looting and killing raids, prompting Christians to form self-defence militias.

The Seleka and other groups have since splintered, prompting further violence even as the country held a democratic election won by President Faustin Archange Touadera who was sworn in in March 2016.

One witness to the recent attacks, identified only as Clement, said advancing fighters from the Fulani Union for Peace in Central Africa (UP) shot four of his children dead including a seven-month-old baby during an attack in March.

Killings by the rival Popular Front for the Renaissance of Central African Republic (FPC) were also reported.

HRW based its tally on interviews with residents in the town of Barbaric in April. It said the overall figure was probably higher since dozens of people are still missing.

Persistent violence

The United Nations, which has a 13,000 safe-keeping mission in the former French colony, sought to disperse fighters with air strikes in Ouaka as they advanced on the town of Barbaric.

The US has imposed sanctions on militia leaders.

Still, the violence persists. Medical charity Doctors without Borders (MSF) said last month that it was the worst seen in a years-long conflict and reported mutilations and summary executions.

READ MORE: Displaced and forgotten in Central African Republic

In December, the UN told Al Jazeera that a recently formed rebel group in the CAR has inflicted havoc in the western half of the country, displacing thousands and emptying towns and villages in a country already hit hard by instability.

The Return, Reclamation, Rehabilitation group, or 3R, was formed in late 2015 and has displaced at least 30,000 people in the Ouham-Pende region in CAR, debilitating relief efforts in the region.

The UN says that the relief efforts in CAR remain underfunded; only 36 percent of the 2016 Humanitarian Response Plan was financed.