GAO, Mali: Mali risks descending into "catastrophic" violence, the UN rights chief warned Tuesday, as tensions swept the country after a string of attacks by Islamist rebels on French-led forces.

After four days of suicide bombings and guerrilla fighting in the northern city of Gao, fears of fresh attacks were high following a call from Al-Qaeda in the Arabian Peninsula (AQAP) -- which US officials have labelled Al-Qaeda's most dangerous franchise -- for a holy war in Mali.

UN rights chief Navi Pillay warned a second kind of violence also threatened the country -- reprisal attacks by the army and black majority on light-skinned Tuaregs and Arabs accused of supporting the rebel groups that have plunged Mali into crisis.

"As the situation evolves, attacks and reprisals risk driving Mali into a catastrophic spiral of violence," Pillay told the UN Security Council.

"Protection of human rights is key to stabilising the situation."

Pillay said human rights investigators from her department had started arriving in the Malian capital Bamako last week.

Rights groups have accused the Malian army of killing suspected rebel supporters and dumping their bodies in wells.

Tuaregs and Arabs have also come under attack from their black neighbours in northern towns such as Timbuktu, where looting broke out after French-led forces reclaimed the city and a mob tried to lynch an alleged Islamist supporter.

A grave containing several Arabs' bodies was discovered in Timbuktu last week.

Many Arabs and Tuaregs have fled the north, fearing reprisal attacks.

In all, the crisis has caused some 377,000 people to flee their homes, including 150,000 who have sought refuge across Mali's borders, according to the UN.

Mali imploded after a March 22 coup by soldiers who blamed the government for the army's humiliation at the hands of north African Tuareg rebels, who have long complained of being marginalised by Bamako.

With the capital in disarray, Al-Qaeda-linked fighters hijacked the Tuareg rebellion and took control of the north.

Analysts say the crisis has been fuelled by a complex interplay of internal tensions and international factors, including Al-Qaeda's call to global jihad.

Those concerns were underlined Tuesday when AQAP, Al-Qaeda's Yemen-based branch, condemned France's intervention as a "crusader campaign against Islam" and called all Muslims to join a holy war against it.

Around 90 percent of Malians are Muslim, but the Islamist extremists' hardline ideology is not broadly accepted here.

"Supporting the Muslims in Mali is a duty for every capable Muslim with life and money, everyone according to their ability," AQAP's Sharia Committee said in a statement reported by the US-based SITE Intelligence agency.

AQAP said jihad is "more obligatory on the people who are closer" to the fight and that "helping the disbelievers against Muslims in any form is apostasy".

The statements were an apparent reference to north African countries, notably Algeria, where Islamist gunmen attacked a gas field after the government agreed to let French warplanes use Algerian airspace, unleashing a hostage crisis that left 37 foreigners dead.

Al-Qaeda in the Islamic Maghreb, Al-Qaeda's north African branch, is one of the groups that seized control of northern Mali for 10 months in the wake of the March coup, along with the Movement for Oneness and Jihad in West Africa (MUJAO) and Ansar Dine (Defenders of the Faith).

France launched its intervention on January 11, after Mali's interim government called for help fending off the Islamist insurgents as they advanced into southern territory.

But after pushing the rebels from the towns under their control, France is eager to wind down the operation in its former colony and hand over to United Nations peacekeepers.

In Gao, the largest city in the north -- hit by back-to-back suicide bombings and an hours-long street battle in recent days -- troops from Mali and Niger were patrolling the nearly empty streets, brusquely interrogating the few people they encountered.

A Malian officer said they had made "several arrests".

French and Malian troops have warned snipers may still be lurking in the city, where a French attack helicopter on Monday destroyed the building the Islamists used to stage their assault.

The Malian army also reclaimed control Tuesday of the northeastern town of Menaka, which Tuareg rebels had re-occupied a week ago.

A Malian military source said the town was recaptured with no fighting.

The European Union said it would resume aid to Mali worth up to 250 million euros that was suspended after the coup.

Britain also announced aid of £5 million ($7.8 million, 5.8 million euros) for food, medical supplies and clean water for civilians caught up in the conflict.