Tchenguiz now owns a 6.09% stake in the company, up from 5.08%.
Tchenguiz with Coast Capital Management, FirstGroup's second biggest investor with a 10% holding, called for the sale in November, saying Aberdeen-based FirstGroup's U.S. assets had no synergies with its operations at home, which include a bus and rail division.
FirstGroup said in December it was exploring options including a potential sale for its North American contract businesses, which could result in it exiting the country. It put up its North American intercity bus service, Greyhound, for sale last year.
(Reporting by Noor Zainab Hussain in Bengaluru; Editing by Shinjini Ganguli)