US prosecutors have dropped charges against a Mississippi man accused of sending ricin-laced letters to President Barack Obama, a US senator and a state judge.

The decision came hours after Paul Kevin Curtis, 45, was released from a Mississippi jail on bond.

Mr Curtis, who is known in Mississippi as an Elvis impersonator, told reporters he respected Mr Obama.

"I would never do anything to pose a threat to him or any other US official," he said. "I love this country."

He said he had no idea what ricin was.

"I thought they said rice, I told them I don't eat rice," he said.

Prosecutors said the "ongoing investigation has revealed new information," but provided no additional details.

Later, investigators in the case searched the house of a second Mississippi man.