At least 29 people, including six Canadians, were killed in an attack on a top hotel in the capital of Burkina Faso, the latest country to be drawn into a regional jihadist battle against the West and its allies.
A family statement on Sunday says surgeon Ken Elliott and his wife Jocelyn disappeared on Friday night.
President Roch Marc Christian Kabore, who took office just last month, a year after a popular uprising ousted longtime leader Blaise Compaore, called on his fellow citizens to show "courage".
Yesterday's violence mirrored an attack on the Radisson Blu hotel in neighbouring Mali in November that left 20 people dead.
At least 13 foreigners were among the 29 people killed in the hours-long attack on the cafe and four-star Splendid hotel.
"There is a very strong political will on the part of the two states to combine our efforts to fight terrorism", said Burkina Faso's prime minister, Paul Kaba Thieba.
Al-Qaida is claiming responsibility, saying it is "revenge against France and the disbelieving West".
But he added that the people of Burkina would "always emerge victorious".
In this image taken from video from AP Television, a freed woman, center, walks past French special forces near the Splendid Hotel, early Saturday, Jan. 16, 2016, in Ouagadougou, Burkina Faso.
One survivor of the attack at the Cappuccino restaurant said that diners first mistook the shots and explosions for firecrackers before two gunmen burst in dressed in black and brandishing assault rifles.
A restaurant opposite the hotel was also attacked and a staff member, reached by telephone, said several people had been killed, but was not able to give an exact toll.
The US citizen has been named as Michael Riddering, a missionary who moved with his wife to Burkina Faso to run an orphanage.
The couple both grew up in the WA country, with Dr Elliot leaving school at 15 to work on his family's farm.
Burkinabe forces backed by French soldiers based in neighboring Mali managed to help free at least 126 hostages though officials have said the true number of those held hostage may be higher.
Three attackers were killed at the hotel and a fourth was killed when security forces cleared out a second hotel nearby. The doctor and his wife are in their 80s.
"During the Ebola crisis, when it was hard to find people to do the digging, Mike would go out and join them so they could continue doing the work", Anderson said.
Swiss authorities said its two nationals who were killed were also in Burkina Faso for humanitarian reasons.
It's not yet known why, but it's believed they are still alive.
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