The Central African Republic on Thursday announced a 15-day emergency as armed groups tried to blockade the capital Bangui in a bid to topple newly re-elected President Faustin Archange Touadera.

Rebels controlling about two thirds of the perennially volatile nation launched an offensive a week before presidential elections on December 27, trying to blockade Bangui and carrying out several attacks on key national highways.

"The state of emergency has been proclaimed across the national territory for 15 days, starting from midnight (2300 GMT)," presidential spokesman Albert Yaloke Mokpeme said over national radio.

He told AFP the state of emergency would also allow authorities "to make arrests without going through national prosecutors".

Touadera was declared re-elected by the constitutional court on Monday, though two voters out of three did not cast their ballot, mainly due to insecurity in a country caught up in civil war for eight years.

Attacks on supply convoys by militia groups and their political allies, including former president Francois Bozize, are risking supplies of food, medicine and resources for services such as hospitals, said Vladimir Monteiro, spokesman for the UN's mission, known as MINUSCA.

On January 13, the rebels launched two simultaneous attacks on Bangui but were rebuffed by MINUSCA, which has been present in the country since 2014.

"Since the thwarted offensive of the 13th, there haven't been any other attacks, just incidents linked to the curfew," said lieutenant-colonel Abdoulaziz Fall, one of the MINUSCA spokesmen.

The price of some basic commodities has increased by at least 50 percent in some places.

Touadera's government controls only about one-third of the former French colony, with militia groups that emerged from a conflict in 2013 controlling the remainder of the territory.

CAR prosecutors have launched an investigation into former president Bozize, accused by the government of plotting a coup with the help of armed groups ahead of the elections.

Bozize, who denies the allegations, came to power in a coup in 2003 before being overthrown in 2013, after which the country slid into sectarian conflict.

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