INDIANAPOLIS – The search for what caused a massive, deadly explosion that rocked an Indianapolis neighborhood turned to natural gas Monday, with officials checking gas lines and a homeowner saying a problem furnace could be to blame.

The National Transportation Safety Board sent investigators to check gas main and other lines serving the neighborhood where two people were killed and seven injured in the weekend blast. Local gas supplier Citizens Energy said it also was checking gas lines and a meter at the home that exploded.

But officials cautioned that it was too soon to rule out other causes, saying only that they do not believe a meth lab was to blame for the explosion that obliterated two homes and severely damaged dozens of others.