Federal agents have arrested a Mississippi martial arts instructor over America's ricin investigation.

Everett Dutschke was arrested at his home in Tupelo, Mississippi after charges were dropped against another Mississippi resident who Dutschke allegedly had links to.

Dutschke's home and business premises were also searched by federal agents.

The deadly poison was posted to a number of politicians last week includign one envelope which was addressed to President Barack Obama.

The envelopes were intercepted before they reached their targets.