ABIDJAN, Ivory Coast (AP) — Ivory Coast will be gradually withdrawing its military contingent from the U.N. peacekeeping mission in Mali after failing to secure the release of 46 Ivorian soldiers who have been accused of being mercenaries.

The announcement was made in a letter, which was sent to the U.N. secretary-general last week and circulated Tuesday.

In the letter to the U.N., Ivory Coast officials said they wouldn't replace their personnel in MINUSMA when the current group rotates out in August. Ivory Coast had 857 personnel serving in Mali as of June.

Negotiations have stalled over the release of the Ivorian soldiers, who were arrested at the airport on arrival in July. Three female soldiers have been released, but the others remain in Malian custody.

The Ivorian soldiers were sent to Mali to work for Sahelian Aviation Services, a private company contracted by the United Nations.

However, Mali’s government said it considered the Ivorians to be mercenaries, because they were not directly employed by the U.N. mission and charged them with undermining state security. Malian authorities said the aviation company should “henceforth entrust its security to the Malian defense and security forces.”

The detention of the Ivorian soldiers marked the latest sign of tension between Mali’s leader and the international community. Col. Assimi Goita has faced growing isolation after he seized power in a coup two years ago and then failed to meet an international deadline for organizing a new democratic election.

On Monday, the U.K. announced it would be withdrawing its 300 peacekeepers from Mali, saying the country’s growing reliance on Russian mercenaries is undermining stability.

France, the one-time colonial power that had fought Islamic extremism for nine years in Mali, completed its troop withdrawal from the country earlier this year.