The International Criminal Court's chief prosecutor on Monday welcomed the arrest of an alleged militia commander in the Central African Republic, but said she remained "very concerned" about the country's volatile situation.

Mahamat Said Abdel Kani, an alleged leader of the Seleka rebel coalition, was handed to the court on Sunday and arrived at the ICC's detention unit in The Hague early Monday, court officials said.

Kani, 50, is suspected of committing crimes against humanity and war crimes including torture after the country spiralled into sectarian violence in 2013, following the ouster of former leader Francois Bozize.

The violence pitted the Seleka, a mainly Muslim-backed rebel coalition against mainly Christian vigilante self-defence groups known as anti-Balaka, which means anti-machete.

"We will continue to exert all efforts to hold to account those responsible for atrocity crimes in CAR, irrespective of which side of the conflict they may be on," the ICC's prosecutor Fatou Bensouda said in a statement.

Two other suspects in the violence in the Central African Republic are currently on trial at the ICC.

Bensouda added she "remain very concerned about the security situation and reports of serious violence and crimes committed against civilians, as well as international peacekeepers."

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

Bangui's declaration came hours after the UN envoy to the country called on the Security Council to agree a "substantial increase" in the number of peacekeepers deployed there in response to deadly violence.

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

jhe/dl