The ship sent a message on the United Kingdom Maritime Trade Operations portal saying five to six unknown armed personnel had boarded on the evening of January 4, the Indian navy statement said.
The Ruen last reported its position off the coast of Somalia on Monday at 1810 GMT, according to data from ship tracking and maritime analytics provider MarineTraffic.
Iran is increasing its threats to shipping and also seeking to harass US naval forces in the Persian Gulf and Gulf of Oman.
Blackbeard and his crew cruised through the Caribbean, gaining notoriety and acquiring treasures that remain undiscovered to this day.