"These populations urgently need better security", Nesirky said at a daily news briefing here, Xinhua reported. He, however, did not disclose more details on these armed groups.
"The agency (UN Refugee Agency) said that and its partners are responding through protection-by-presence, humanitarian assistance, advocacy for protection measures and in exceptional cases, through facilitating the movement of these communities to safe sites," he said.
"But it says that humanitarian efforts alone cannot be a sufficient solution to the crisis."
"The UN Refugee Agency is appealing again to all armed elements to stop indiscriminate attacks against civilians," he said. "It is also calling for the deployment of more international troops."
Thousands of people are estimated to have been killed in the conflict in CAR, which erupted when mainly Muslim Seleka rebels launched attacks in December 2012 and has taken on increasingly sectarian overtones as mainly Christian militias known as anti-Balaka (anti-machete) have taken up arms.
Since December 2012, violence and instability have displaced more than 700,000 people inside the CAR and forced more than 288,000 to flee to neighbouring Cameroon, Chad, the Democratic Republic of Congo and the Republic of Congo.