Updated

More than three dozen people remain unaccounted for almost a week after the end of the four-day terrorist attack on Nairobi's Westgate Mall that killed at least 67, the head of the Kenyan Red Cross said Monday.

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.

At least 61 civilians and 6 security troops were killed in the attack.

Government reports on the number of terrorists killed, however, have been confusing and at times contradictory.

President Uhuru Kenyatta said last week that five attackers had been killed by security forces' gunfire and his office said one or more might be trapped under the building's rubble.

In an interview on Citizen TV late Sunday night, however, Interior Minister Joseph Ole Lenku said that two attackers had been hit by gunfire and that the building was thought to have collapsed on three others.

Later in the interview he said all five Islamic extremist members were thought to be under the rubble, and that no bodies of any terrorist suspects had been recovered.

"We are sure they never got out of the building, so let the forensic examination establish the exact truth," he said.

When pressed about the government's initial estimate that 10 to 15 terrorists could have been involved in the attack, Lenku conceded that the figure could have been wrong, or that some could have escaped.

"We do not rule out the possibility that when we were evacuating people in the first stages of the operation it is possible some could have slipped out," he said. "And that is why we are holding a number of people for interrogation; that is why we immediately sealed off the points of exit, the airports."

The Red Cross number of missing 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.

The Nairobi city morgue said it had no remaining bodies recovered from the Westgate attack as of Friday.

Lenku on Sunday 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.

In the television interview later Sunday, Lenku indicated it was possible people were reporting the missing to the Red Cross and not to the police.

"Why is this not being reported to the police?" he asked. "Kenyans must learn to use the government machinery to do their report."

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.

Kenyan authorities have detained a total of 12 people in connection with the attack under the country's anti-terrorism laws, including one on Sunday. Three people have been set free, including a British man who was reported arrested last week as he tried to board a flight from Nairobi to Turkey with a bruised face, the British Foreign Office confirmed Monday.

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 Qaeda-linked militant group that had seized large parts of that country for years before being dislodged from the capital, Mogadishu.