Gunmen have shot dead 13 civilians in an attack on a remote village in troubled Central African Republic (CAR), local officials said on Tuesday.

Around 20 rebels on Monday attacked Diki, near the Chadian border in the northwest of the country, according to regional prefect Jean Gilbert Gbangoudou.

The village mayor, Ibrahim Senoussi, confirmed the death toll and said two people were also wounded.

The assault took place some 22 kilometres (14 miles) from an army base in Bamingui-Bangoran prefecture, although the soldiers were only alerted afterwards, local deputy Aline Aziza told AFP.

The rebels gathered "the men of the village, saying they wanted to talk to them" and then opened fire, Senoussi said.

"The women and children then fled into the bush."

There was no immediate response from the CAR government and the UN peacekeeping mission MINUSCA to an AFP request for information.

Landlocked, mineral rich but deeply poor, the CAR is one of the world's most turbulent countries, struggling with a decade-long burden of civil strife.

The bloodshed came a day after a referendum on a new constitution that would allow President Faustin-Archange Touadera, 66, to seek a third term.

The main opposition parties, civil groups and armed rebels all called on voters to boycott the exercise, accusing Touadera of seeking to remain president for life.

The proposed constitution would extend the presidential mandate from five to seven years and abolish the two-term limit.

In 2020 Touadera won a second five-year term after a vote overshadowed by an offensive by armed rebel groups.

They were thwarted by hundreds of Rwandan troops and operatives from Russia's Wagner mercenary force, who have largely pushed rebel groups into rural areas.