Kenya Red Cross has said it has received reports of 39 people still missing after the attack on a shopping centre in Nairobi.
It follows the Kenyan Interior Minister's announcement on Sunday that he does not believe there are any more hostages inside the building.
Kenya Red Cross said it is in continual contact with the relatives of those reported missing, but that 39 people have still not been accounted for.
A total of 67 people have been confirmed dead as a result of the attack.
Police are investigating whether some of the Westgate Mall attackers were able to escape through an underground tunnel, sources have told ITV News.
Africa Correspondent Rohit Kachroo reports from Nairobi:
The latest question for Kenyan authorities is over an apparent warning made about an attack here around a year ago. The question: Was prior intelligence ignored?
Today the government has been speaking only about progress: Saying they have recovered one of the terrorists' cars. They say they are now certain there were 10 to 15 militants involved and that five were killed by gunfire.
But that raises another question: What happened to the others? Were they all detained or did some escape?
I understand that one theory being taken seriously by the police here is that some used their knowledge of the site and an underground tunnel to get away during the early hours of the raid.
Kenya's Interior Minister has said he does not believe there were any hostages left in the shopping centre "unless forensic evidence shows otherwise".
There are nine suspects in custody over the attack on a mall in Nairobi, Kenya's Interior Minister has said. One suspect was arrested today, he added.
One of the soldiers in the three-day long assault by Kenyan forces against al-Shabaab militants inside the Westgate Mall has described his experience.
He said the fighters were "more than professional" and that one of the attackers was "certainly" a woman, as Africa Correspondent Rohit Kachroo reports.
One of the soldiers involved in the three-day long battle inside the Westgate Mall described his opponents, the militants, as being "more than professional." He describes them quickly advancing then retreating as they fired indiscriminately through the corridors of the Westgate Mall.
He didn't get a glimpse of the attackers but he said that one of them was certainly a woman, he heard her voice, and he heard her scream on Monday before detonating what he believes to have been a suicide device.
The Kenyan Interior Ministry has said no more bodies have been found in the Westgate shopping mall. It said the government is continuing to work with Interpol, adding that the death toll stands at 67, including 61 civilians and six security guards.
No bodies have been recovered.
We're giving the position of govt. The death toll till stands at 67. 61 civilians and 6 security officers.
We're working together with Interpol. We don't want to divulge their work until we get a final report.
Kenyan authorities are holding eight suspects over the Westgate mall attack, and have released three people after questioning, according to the Kenyan interior minister.