Four United Nations (UN) peacekeepers from Bangladesh were killed in central Mali on Wednesday after their vehicle hit an explosive device and four others were seriously injured, the UN said.

Mali mission chief Mahamat Saleh Annadif said the peacekeepers hit the device along the Boni-Douentza road in the Mopti region.

He said six Malian soldiers were also killed in a similar manner on Tuesday in the Segou region.

UN Secretary-General Antonio Guterres strongly condemned the attack against the Bangladeshis and reiterated that attacks targeting UN peacekeepers may constitute war crimes under international law, the body's spokesman Stephane Dujarric said.

Guterres demanded that the perpetrators be apprehended and prosecuted, he said.

The more than 11,000-strong mission in Mali has become the most dangerous in the world for UN peacekeepers, which are routinely attacked by militants. The threat of groups related to al-Qaida and the Islamic State group continues to spread through Mali.

Annadif said the Mali mission is strengthening its security systems in central Mali.

Guterres said the “cowardly acts” that killed the Bangladeshi and Malian soldiers will not deter the UN mission's “determination to support the Malian authorities in their efforts to protect civilians and accompany the Malian people in their quest for peace and stability,” Dujarric said.