© Jérôme Delay/APMalian soldiers on patrol in the capital Bamoko.
At least 53 soldiers and one civilian died in the attack on an isolated military base in the north-east of the country, the government said.
The authorities first reported the attack in Indelimane, in Menaka region, on Friday, but gave a lower provisional death toll.
"Heavily armed unidentified men attacked around noon. The attack started with shellfire ... Then they retreated toward Niger," the government spokesman Yaya Sangare said.
Sangare said the death toll was unclear because the bodies were still being identified, and that the army was undertaking a combing operation on the ground with support from international forces, including French troops and UN peacekeepers.
"The dispatched reinforcements found 54 bodies including one civilian, 10 survivors and considerable material damage," Sangare said on Twitter earlier on Saturday.
Local media reported that after an initial bombardment, the positions of the Malian soldiers were over-run by small groups of militants, some riding motorbikes. Only 20 soldiers survived the assault.
There has been no claim of responsibility, but the attack follows a series jihadist raids in late September that underscored the increasing reach and sophistication of armed groups operating in the region.
From their stronghold in Mali, groups with links to al-Qaida and Islamic State have been able to strike across the Sahel, destabilising parts of Niger and Burkina Faso.
Thirty-eight Malian soldiers were killed on 30 September in coordinated attacks on two army bases in the centre of the country, which has slipped from government control despite the presence of French army units and other international forces.
Around 20 people were killed last month in an attack on a gold mining site in neighbouring Burkina Faso, suggesting the violence continues to spread.
The G5 Sahel, a joint taskforce, was created in 2014 to try to tackle the problem, backed by the region's former colonial power, France. It has pooled troops from Burkina Faso, Chad, Mali, Mauritania and Niger since July 2017 in a bid to drive back the jihadist groups.
But a lack of finance, training and equipment limited their effectiveness and their numbers. The force numbers 4,000 troops although 5,000 were originally planned.
Two hundred and fifty highly trained British ground troops are scheduled to be deployed to reinforce the UN peacekeeping mission in Mali in 2020.
The UN has struggled to defeat the militants, though has succeeded in pushing groups into remote areas.
The militants have been active in the Sahel for more than a decade and have built close ties with some local communities by carefully exploiting ethnic and other communal divides.
Mali is the most dangerous country in the world for UN peacekeepers. So far 123 have died and 358 have been severely wounded in the ongoing counterinsurgency operations.
It is much more dangerous for Malian citizens, who face a deepening humanitarian crisis. "Violence and insecurity have escalated to unprecedented levels" in parts of Mali and nearby countries, the UN said in May.
The British troops are expected to be based in the north-eastern city of Gao. The deployment comes at the request of the UN mission in Mali, known as Minusma.
France has had around 4,500 combat troops in the region since 2012, when militants captured the city of Tombuctou and threatened to advance into the centre of Mali.
Minusma issued a statement condemning the attack. An operation to restore security was under way, the UN said.
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