Four international aid agencies have temporarily suspended their operations in northern Central African Republic due to attacks on aid workers by armed groups, the United Nations said.

In the country's Ouham region, aid workers have been attacked on 16 occasions since March, the UN Office for the Coordination of Humanitarian Affairs (OCHA) said on Friday.

"It is one of the most dangerous and difficult countries for humanitarian work, particularly in the northern prefecture of Ouham," OCHA spokesman Jens Laerke said, adding that there had been a recent concentration of attacks against aid workers.

"This temporary withdrawal will certainly have an impact on many people who depend on aid," he told a news briefing in Geneva.

Solidarites International, Intersos, Danish Church Aid, and Person in Need Relief Mission will withdraw their staff to the capital, Bangui, while other aid groups have decided to scale back to focus only on life-saving operations, according to OCHA.

Central African Republic has been plagued by conflict since March 2013, when mainly Muslim Seleka rebels seized power, triggering reprisals by Christian "anti-balaka" militias.

The Seleka and other groups have since splintered, prompting further violence despite the election in March 2016 of President Faustin-Archange Touadera, which raised hopes of reconciliation.

IN PICTURES: Displaced and forgotten in Central African Republic

Around 425,000 people have been uprooted by the fighting within the Central African Republic, some 465,000 have fled to neighbouring countries, and more than 2.2 million, nearly half the population, need humanitarian aid, according to OCHA.

The lives of more than one million children are under threat amid a lack of funding, said the UN children's fund (UNICEF).

More than 40 percent of children are suffering from chronic malnutrition, one in seven will die before they turn five, and a third are out of school, according to figures from UNICEF.

The country's humanitarian response plan for 2017 has only been 12 percent funded - $47m of a requested $400m - to date, the UN's Financial Tracking Service (FTS) shows.

"We cannot allow the Central African Republic to become a forgotten crisis," Christine Muhigana, UNICEF representative in the Central African Republic, said in a statement.