Federal safety officials are investigating the role of a natural gas pipeline in a fatal blast at a Pennsylvania chocolate factory, the National Transportation Safety Board announced Tuesday.

Friday's powerful explosion at R.M. Palmer Co. killed seven people, sent 10 to the hospital and damaged several other buildings in West Reading, a small town 60 miles (96 kilometers) northwest of Philadelphia, where the 75-year-old, family-owned company has long had a factory.

The National Transportation Safety Board announced the probe late Tuesday afternoon, calling the incident a “natural gas” explosion and fire. The agency has preliminary information from local authorities and a natural gas utility that a gas pipeline was involved, an agency spokesperson, Keith Holloway, told The Associated Press.

NTSB is investigating “what caused, how and why the explosion occurred,” according to Holloway.

Other local, state and federal investigations are ongoing.

Pennsylvania State Police have said “everything’s on the table” as fire marshals also try to pinpoint the origin and cause. Some workers told relatives they smelled natural gas before the blast, although the gas utility UGI said it received no reports of a gas leak.

“UGI is cooperating with authorities in the investigation concerning the incident at R.M. Palmer,” utility spokesperson Joe Swope said late Tuesday. He directed further questions to the NTSB.