No one has claimed responsibility for the assault in the central town of Sevare, which coincided with a surge in jihadist attacks spreading through the region in recent months.
"At this stage there is no formal proof that it was the Macina Liberation Front (FLM), but strong suspicions point to this group that has been seeking notoriety at all costs," the source said.
Since it first appeared earlier this year the FLM has claimed responsibility for several attacks, including some targeting security forces in central Mali.
The United States placed Ansar Dine on its terror blacklist in 2013, accusing it of close links with Al-Qaeda and of torturing and killing opponents in the north.
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The private Mauritanian news agency Al-Akhbar, which regularly publishes jihadist statements, also said Sunday that the FLM "could be behind the attack in Sevare."
The deadly siege began early Friday when gunmen burst into the Hotel Byblos, frequented by expatriates.
Reports vary on the numbers and identities of those killed.
The UN mission in Mali (MINUSMA) said two Ukrainians, a Nepalese and a South African were killed during the siege and subsequent military operation, as well as a Malian driver working for a company contracted by the mission.
An army officer said "five terrorists" were killed in the operation as well as five soldiers and "two whites".
Four of the soldiers were buried in Sevare yesterday, with the rural development and security ministers, Boukary Treta and Sada Samake, in attendance, a witness said.