Central African Republic (CAR) declared a state of emergency on Thursday to help it crack down on armed groups, as the United Nations' envoy to CAR called for the deployment of many more peacekeepers in response to a recent surge in attacks.

The CAR army, backed by UN, Russian and Rwandan troops, has been battling rebels that are seeking to overturn a December 27 vote in which President Faustin-Archange Touadera was declared the winner.

The state of emergency, which will last 15 days, lets the authorities fast-track arrests by allowing the military to detain suspects without going through a prosecutor, government spokesperson Albert Yaloke said in a statement.

The escalation comes as UN envoy Mankeur Ndiaye asked the UN Security Council for a substantial increase in the number of peacekeepers to give the mission greater mobility on the ground.

The country "is at serious risk of a security and peacebuilding setback," Ndiaye said in an address to the council earlier on Thursday.

Seven peacekeepers have been killed since the rebels launched their offensive last month. The fighting has forced nearly 60 000 people to flee the country, compounding an already dire refugee crisis.

Ndiaye said large numbers of CAR troops had deserted due to insufficient training and resources.