The move against former defense secretary Gotabaya Rajapaksa is the toughest sanction yet on a member of the family that ruled the Indian Ocean island until a surprise election defeat in January.

It is part of a wide probe of alleged corrupt deals and repression by the former president and his relatives.

Police this year seized more than 3,000 weapons in 20 containers from the armory, run by private security firm Avant Garde Maritime Services (Pvt) Ltd and docked in the southern port of Galle.

"The Galle magistrate imposed a travel ban on three people: former secretary of defense Gotabaya Rajapaksa; former navy commander and adviser of Avant Garde, Satilaka Dissanayake; and another director of Avant Garde," acting police spokesman Ruwan Gunasekara told Reuters.

The armory was a commercial venture that stored weapons for maritime security guards stationed on ships that pass near Sri Lanka, located on one of the world's busiest sea routes.

The loosely regulated practice of arming merchant ships has flourished in recent years in response to the threat of piracy.

Gotabaya Rajapaksa, who oversaw the military defeat of Tamil Tiger separatists after a 26-year war, is also being investigated by police over abductions, assaults and murders during his brother's time in office.

Government spokesman Rajitha Senarathne accuses Gotabaya Rajapaksa of maintaining a "private military" with the floating armory. Gotabaya Rajapaksa, who has previously denied wrong doing, was not immediately available for comment.