The Red Cross' report of 39 missing people conflicts with the government's contention that there are no remaining missing people from the attack that began Sept. 21, and suggests that the death toll could still rise as investigators dig through the rubble of the partially collapsed mall.
"The numbers with us are what we are still showing as open cases that are reported to us," Red Cross head Abbas Gullet told The Associated Press by telephone.
"The only way to verify this is when the government declares the Westgate Mall 100 percent cleared - then we can resolve it," he said.
The Red Cross number has been dropping over the past week as bodies have been positively identified and as some missing people have been reunited with their families, Gullet said.
The Red Cross said Friday the number of missing people stood at 59.
As of Monday, however, the Nairobi city morgue had no remaining bodies from the Westgate attack, he said.
On Sunday, Interior Minister Joseph Ole Lenku told reporters that police had no missing persons reports from the mall attack, and that authorities did not believe there were any hostages in the mall building when it partially collapsed.
He left open the possibility, however, that things might change.
"We think - unless the forensic investigation shows otherwise - we really do think that there were weren't any hostages," he said.
FBI agents, along with investigators from Britain, Canada and Germany, are participating in the investigation into the attack and are aiding Kenyan forensic experts poring through the mall complex. Results are not expected until later this week at the earliest.
In addition to the 61 civilians and 6 security troops reported killed in the attack, the government has said five of the attackers were killed by gunfire and at least one more is thought to be in the building's rubble.
The militant group al-Shabab has said it carried out the mall attack to punish Kenya for sending its troops into neighboring Somalia to fight the al-Qaida-linked militant group that had seized large parts of that country for years before being dislodged from the capital, Mogadishu.