A New York man accused of plotting to set off homemade explosives he had stashed at sites across Manhattan has been indicted, federal prosecutors said.

Michael Gann, 55, allegedly built at least seven improvised explosive devices last month using chemicals purchased online in May. The bombs were placed on the rooftops of adjoining residential buildings and thrown onto subway tracks, according to an indictment handed up by a grand jury.Gann was arrested in early June near the buildings, possessing one of the devices.

No injuries were reported from any of the devices.

Prosecutors stated that Gann put "countless lives at risk" by his actions.

Jay Clayton, the interim US attorney for the Southern District of New York, noted the severity of the charges.Gann faces up to 40 years in prison if convicted on all counts.

A judge ordered his detention following a bail hearing.

His lawyer, Martin Cohen, declined comment.

The case highlights ongoing concerns about terrorism and public safety in urban areas.