"There's a significant number of homes that have sustained damage, including two that have been completely destroyed, no cause has been ruled out," said Marc Lotter, a spokesman for Indianapolis Mayor Greg Ballard.

"The investigation is ongoing," he said. He added that seven people had been injured in the explosion, which left a large debris field and damaged at least 18 houses in addition to the two that were destroyed.

An Indianapolis Fire Department spokeswoman said none of the injuries were life-threatening.

The identities of the victims have not yet been released, Lotter said. (Reuters)