Grenade attacks in Central African Republic's Bangui killed at least two people late on Wednesday in a rare incident of violence in the capital, the United Nations and residents said.

Men on motorbikes threw grenades into crowds gathered in three different places in southern Bangui during the evening, residents said.

"MINUSCA strongly condemns these odious and cowardly acts that killed two people and injured numerous others," the U.N. mission said in a statement late on Wednesday.

An aid official with medical charity Medecins Sans Frontieres said at least 20 people were wounded. A relative of one of the victims said one wounded person had since died, bringing the death toll to three.

Thousands of Central Africans have died and hundreds of thousands remain displaced after two years of violence that erupted after mainly Muslim Seleka rebels seized power in the majority Christian country in 2013.

The capital Bangui, secured by French and U.N. soldiers, had not seen attacks for months.

Voters are due to go to the polls on Oct. 18 to choose a new president and parliament to replace an interim government led by Catherine Samba-Panza.

But preparations are running behind and the head of the interim parliament said the polls are likely to be postponed again.

Some analysts have warned that the country is not ready for elections and say they should be delayed to allow transitional authorities to make further progress on disarmament.