The Old City building ravaged by a fire last week will stand for a while longer to give investigators an opportunity to search the wreckage for clues to the blaze's cause, officials said Sunday.

Philadelphia's Department of Licenses and Inspections reported that work at properties adjacent to 239 Chestnut St. needed to be done before demolition could begin but said that the process of tearing down the building would likely begin this week.

Investigators working to determine the fire's origin and cause, though, were unwilling to commit to that schedule, saying demolition would not begin "in the foreseeable future," according to a statement from a spokeswoman for the federal Bureau of Alcohol, Tobacco, Firearms, and Explosives.

The 239 Chestnut building and one adjacent must be reinforced to allow investigators to go inside, the spokeswoman said.

"It will take a few days to make the building safe to enter so ATF and the Philadelphia Fire Marshal's office will continue to follow any leads developed outside the structure," said Charlene Hennessy, the ATF spokeswoman.

The fire began 3 a.m. Feb. 18 and displaced 150 people. The building where it started has been ruled a total loss, and a number of nearby properties still have not been cleared for people to enter. Those buildings include a vape shop, apartments that are home to 60 people, and the restaurant Little Lion.

Neighbors reported hearing an explosion the night of the fire. Investigators have heard the same accounts, Hennessy has said.