BAMAKO (Reuters) - Gunmen attacked a bank and a prison in the southern Mali town of Banamba in the early hours of Monday, freeing 21 prisoners and looting cash, a security ministry spokesman said.

Amadou Sangho told Reuters by telephone that the assailants had arrived in three armed vehicles and on four motorbikes from Nara, near the Mauritanian border, shortly after midnight.

They stole cash from the vault of the Mali Development Bank before breaking into the prison, he said by telephone. No one was killed but a prison guard remains missing, Sangho said.

Justice Minister Mamadou Ismael Konate said the attackers had wanted to release “two terrorists” from prison but that they had already been moved to another town.

It was not immediately clear who was behind the raid, but Islamist groups such as Ansar Dine have stepped up their insurgency in Mali this year, carrying out more than 60 attacks on United Nations and other targets since May.

Islamist groups hijacked a separatist Tuareg rebellion in 2012 to seize major towns in Mali’s vast desert north. French forces drove them back a year later, but they have kept bases in remote desert locations and are increasingly spreading their raids south into areas previously deemed safe.

Defense ministry spokesman Abdoulaye Sidibe said that a gendarmerie post in Banamba was also attacked in Monday’s raid.

In a separate attack on Sunday, a Togolese soldier for the U.N. peacekeeping mission and two Malian civilians were killed in a convoy in the Mopti region, a spokesman for the U.N. secretary general said in a statement.

The secretary general urged Malian parties to continue to work to implement a peace deal signed last year between the government and Tuareg-led rebels, which was intended to let the state focus on fighting Islamists but which has since stalled.