People in Burkina Faso are campaigning for the release of an Australian doctor and his wife, kidnapped the same day as the attack on the capital.
Ken and Jocelyn Elliott, who are in their 80s, have built up medical facilities since the 1970s in the town of Djibo near the Mali border.
Locals have started a Facebook page posting messages of support.
It is unclear if their abduction is related to Friday's deadly al-Qaeda attack in the capital Ouagadougou.
Burkina Faso's government says 28 people were killed and a further 56 injured in the attack, which targeted two hotels and a cafe frequented by foreign nationals. Six of the dead were from Canada.
Hamadou Ag Khallini, a spokesperson for Malian militant group Ansar Dine, told Australian media that the al Qaeda-linked Emirate of the Sahara group were holding the couple.
The group operates in northern Mali.
No reason for the abduction has yet been given and the couple's whereabouts are unknown, Australia's foreign ministry said.
The couple were running a 120-bed clinic in the town of Dijbo, where Dr Elliot is the only surgeon.
Djibo residents have set up a Facebook page called "Djibo supports Dr Ken Elliot" to describe the impact he and his wife have had on the town.
Analysis - Thomas Fessy, BBC West Africa correspondent, Ouagadougou
This latest kidnapping bears signs of an operation mounted by al-Qaeda in the Islamic Maghreb (AQIM). The extremist group has a long history of kidnap-for-ransom in the region, to the extent that it once was one of its major revenue sources.
Similarly, the attack on the cafe and hotel popular with foreigners in the capital was carefully planned. Throughout the siege, AQIM was releasing statements about its intentions to kill as many Westerners as possible.
The intervention of French special forces was key to retaking control of the hotel but this latest attack is another blow for France's military strategy in the Sahel. The French drove most jihadi groups out of their hideouts in northern Mali but AQIM and others remain an active threat throughout the region.
Former Burkina Faso President Blaise Compaore had forged some kind of relationship with these groups, often negotiating the release of foreign hostages. But since he was ousted in a popular uprising, Burkina Faso may have become just another battleground for the Islamist militants.
The Facebook page says Dr Elliott's "numerous patients are waiting for him".
"Elliott is all for us and we need him like a baby needs his mother," said resident Moussa Dicko, quoted on the page.
"Elliott is a Burkinabe and a humane person," said Francois Ramde. "He represents the best of humanity."
"Let the name of God not be used in connection with this ignoble act because it was God who sent Elliott to us and will bring him back," said Roots Hassane.
Militant groups in the Sahel region of north and west Africa have long used kidnap for ransom as a way of raising money.
Friday's attack in Ouagadougou was claimed by AQIM on behalf of one of its affiliates, al-Murabitoun, which is run by the notorious Algerian extremist Mokhtar Belmokhtar.
Last April, al-Murabitoun claimed to have abducted a Romanian security manager who was working at a mine in the north of the country.