UN Secretary General Ban Ki-moon has denounced the "horrific terrorist attack" at a luxury hotel in Mali, warning that the violence is targeting peace efforts in the country.

“The secretary general deplores any attempt to derail the implementation of the agreement” signed in June between rival factions in Mali, Ban’s spokesman Stephane Dujarric said on Friday.

Ban's condemnation came in the wake of a nine-hour hostage crisis in the Radisson Blu hotel in the country’s capital, Bamako, early in the day. The hostage crisis ended with 21 dead.

Citing Ban, Dujarric said that incident took place at a time when a fragile peace process is “making good progress” in Mali.

The UN chief expressed "his full support to the Malian authorities in their fight against terrorist and extremist groups" and said UN peacekeepers from the UN mission in Mali, known as MINUSMA, were on hand to help, Dujarric added.

A militant group affiliated with al-Qaeda reportedly claimed responsibility for the attack and hostage-taking.

Al-Mourabitoun, a group based in northern Mali, posted a message on Twitter saying it was behind the attack on the Radisson Blu hotel.

The Friday hostage crisis took place as the UN has been working to bring back stability to the West African country over the past months.

Northern Mali was occupied by militants, some with links to al-Qaida, for most of 2012. Violence continues in the area despite a French military intervention to allegedly push the militant out .

Peace talks in Algiers this summer resulted in an agreement between Mali’s government and Tuareg-led separatist rebels, which granted greater autonomy to northern regions. However, a variety of armed groups are still operating in the north, including militant offshoots such as al-Mourabitoun, as well as various separatist organisations.