The juntas of Burkina Faso, Mali and Niger have written to the United Nations Security Council to denounce Ukraine's alleged support of rebel groups in West Africa's Sahel region, a copy of their letter showed.

Mali cut diplomatic ties with Ukraine at the start of the month over comments by a spokesperson for Ukraine's military intelligence agency about fighting in Mali's north that killed Malian soldiers and Russian Wagner mercenaries in late July.

The military government of Niger followed suit days later in solidarity with its neighbour.

The dispute broke out after the Ukrainian military intelligence agency spokesperson said Malian rebels had received "necessary" information to conduct the July attack.

Tuareg rebels said they killed at least 84 Wagner mercenaries and 47 Malian soldiers over days of fierce fighting, potentially Wagner's heaviest defeat since it stepped in two years ago to help Mali's junta fight insurgent groups.

Mali and Niger accused Ukraine of supporting "international terrorism".

Ukraine has repeatedly called the allegations groundless and untrue. A Tuareg rebel alliance has also said it did not receive any Ukrainian support.

In their letter to the United Nations Security Council, the foreign affairs ministers of Mali, Niger and Burkina Faso asked it to "take responsibility" for Ukraine's actions and to prevent "subversive acts" that threaten regional and continental stability.

A copy of letter was posted late on Tuesday on the X account of a grouping called the Alliance of Sahel States formed by Burkina Faso, Mali and Niger in the wake of their coups.

Diplomats said the letter was circulated to the 15-member Security Council on Tuesday evening.

Ukraine's foreign ministry did not immediately respond to a request for comment. The country is still locked in heavy fighting with Russia more than two years after Moscow's full-scale invasion.

Burkina Faso, Mali and Niger have turned their backs on traditional Western and regional allies in favour of Russia since their juntas took power over the past four years.