The incident was the first of its kind between Mali, newly backed by Russian forces, and UN peacekeepers, a UN source told AFP on condition of anonymity.

"We are aware of a recent incident in Mali in which rockets were fired by a Malian Armed Forces (FAMa) helicopter close to a detachment of UK personnel," a defence ministry spokesman said in a message to AFP.

"All UK personnel are safe and accounted for, and the circumstances surrounding this incident are being investigated," he added.

The incident took place in the area of Tessit, near Gao city in the east of the country.

According to a diplomatic document seen by AFP, the Malian army fired six rockets from its helicopter.

The document says almost all Malian helicopters are flown by Russians assisted by Malian co-pilots.

The statement questioned whether several MINUSMA contingents could remain in place if Russian troops were involved.

Last week Richard Mills, the US deputy ambassador to the UN, denounced an "unacceptable" incident, which took place on March 22 when a Malian helicopter "fired rockets near peacekeepers in eastern Mali".

United Nations spokesman Stephane Dujarric on Tuesday said a UN investigation into the events was underway.

A team from the UN peacekeeping mission in Sudan is ready to go to Moura in central Mali as soon as the Malian authorities give air access to the area, he added.

According to a diplomat who spoke anonymously, paramilitaries from the Russian company Wagner are suspected to have been involved in this incident alongside the Malian army.

France and other Western nations have denounced the Malian authorities' alleged use of the controversial Russian private security group. The Malian authorities have said they do not use mercenaries.

- Moura 'atrocity' -

Mali is the epicentre of a jihadist insurgency that began in the north of the country in 2012 and spread three years later to neighbouring Niger and Burkina Faso.

Thousands of people across the region have died, and around two million have been displaced.

Attacks have been carried out by militants affiliated to Al-Qaeda or the Islamic State group, but many civilian casualties have also been caused by so-called self-defence forces.

MINUSMA -- the United Nations Multidimensional Integrated Stabilization Mission in Mali -- began its deployment to the troubled Sahel state in 2013.

It has 16,500 personnel, including mostly troops, plus police and civilians, according to its website.

The United Nations says the mission has suffered the most fatalities of any of its peacekeeping operations in the world, with hostile acts causing 159 deaths as of October 31.

Mali's army has been accused of carrying out a massacre in the central town of Moura in late March, with the participation of Wagner mercenaries.

Human Rights Watch has said Malian forces and foreign fighters killed 300 civilians in Moura, in what it called "the worst single atrocity reported in Mali's decade-long armed conflict".

MINUSMA's mandate runs out in June. Several troop-contributing countries are already reviewing their participation in the light of recent developments in Mali.

The EU on Monday decided to halt its military training missions in Mali but will keep a presence in the Sahel, the bloc's top diplomat said.