Chennai, May 16 -- A 64-year-old US citizen was detained at Chennai International Airport on Friday night, becoming the 18th foreign national arrested for allegedly casting an illegal vote in the recently concluded Tamil Nadu Assembly elections.

The passenger, identified as Kishore, a resident of Chennai's KK Nagar holding a US passport, was scheduled to board an Emirates flight to the United States via Dubai around 10:00 p.m. During a routine immigration check, officials noticed the telltale mark of indelible ink on the index finger of his left hand.

Upon initial questioning by immigration authorities, Kishore reportedly admitted to casting his vote in the Virugambakkam constituency of Chennai. Because India does not permit dual citize...