BAMAKO (AFP) - Suspected Islamists on motorbikes killed nine United Nations peacekeepers from Niger on Friday in northeastern Mali, in the deadliest ever attack on the mission, military sources said.

An officer from Niger with the Minusma mission told AFP the ambush had been staged by the Movement for Oneness and Jihad in West Africa (Mujao), an Al-Qaeda-linked militia behind numerous attacks in the restive west African nation.

"This is the deadliest attack against the UN mission in Mali," a statement from Minusma said, adding that aircraft had been deployed to secure the area.

The ambush brought to 30 the number of deaths in the mission since its deployment in July last year.

UN Secretary-General Ban Ki-moon said in a statement he was "outraged" by the attack, which he described as "a serious violation of international law".

Minusma and a senior military official from Niger said the convoy of peacekeepers were on a supply run in the northeastern Menaka-Asongo corridor when they were ambushed by men on motorbikes.

The Nigerien Minusma source said Mujao had formed an alliance with militants from the Fulani ethnic group in the Gao region where the attack took place.

"The terrorists had threatened to carry out attacks in the run-up to the feast of Tabaski. They've just carried them out," added a Malian military source, using the west African name for the Islamic festival of Eid al-Adha taking place on Sunday.

The deaths mark the first losses suffered by Niger's 600-strong force, deployed to Mali in January last year.

"I condemn this attack without reservation. Attacks on representatives of the UN are unacceptable and unjustifiable," said Britain's Africa minister James Duddridge.

"My thoughts and sympathies are with the families and colleagues of those killed and injured in the attack, and with the governments and people of Mali and Niger."

Menaka, an isolated Sahara desert town in eastern Mali crisscrossed by seasonally dry riverbeds, is used mainly as a temporary home by nomadic Tuareg tribes.

It was the scene of heavy fighting between the Mali government and the three main separatist rebel groups in May.

The region of Gao is part of a large swathe of desert which is the cradle of a Tuareg separatist movement that wants independence for the homeland it calls "Azawad", and from which several rebellions have been launched since the 1960s.

Around 50 Malian solders were killed around Menaka and the flashpoint town of Kidal further north by Tuareg and Arab insurgents in May.

Ten UN peacekeepers - all from Chad - have been killed by roadside bombs in the Kidal region in recent weeks, prompting the government in N'Djamena to complain to the UN that the Chadian contingent of Minusma were suffering discrimination.

Mujao claimed responsibility for a rocket attack on a Minusma base close to the border with Algeria in August.

The group joined forces with Al-Qaeda in the Islamic Maghreb (AQIM) and Ansar Dine in 2012 to take control of much of the desert north, including the three main towns of Kidal, Gao and Timbuktu.

They seized power on the back of an uprising by ethnic Tuareg separatists and imposed strict Sharia law and punishments for 10 months, before being ousted from the towns and forced back into desert hideouts by a French military intervention launched in January 2013.

Though order has largely been restored across the territory, Islamist extremists continue to carry out raids and attacks and French troops are still on patrol.

They were also blamed for a suicide attack on August 16 that killed two soldiers from Burkina Faso serving with Minusma in the settlement of Ber, near Timbuktu.

Minusma took over security duties from African troops in Mali in July last year, with a mission to ensure stability in the conflict-scarred nation.

A 12,600-strong force, made up largely of Africans, replaced the AFISMA military mission, which has been supporting the French intervention.

The mission played a key role in presidential polls which saw Ibrahim Boubacar Keita rise to power in August 2013.