QUITO (Reuters) - Ecuadorean prison director Cosme Damian Parrales Merchan was killed on Sunday, the South American country's SNAI prisons agency said in a statement, even as citizens head to the polls to vote in a referendum over a raft of security measures.

       SNAI did not give more details on the death of Parrales, who headed the Manabi No. 4 prison in the west of the country. The agency said it would work with the investigating authorities to determine those responsible.

       (Reporting by Alexandra Valencia; Editing by Josie Kao)