LONDON (Reuters) - Indian Oil Corporation (IOC.BO), India's largest company by revenues, is the bidder behind the approach to UK-listed Gulfsands Petroleum (GPX.L), a source close to the situation confirmed on Sunday.

The Syria-focussed oil explorer last week rejected an unsolicited takeover approach of around 350 pence per share, saying the proposal was "wholly inadequate".

The company, whose shares closed at 308 pence on Friday, is due to upgrade its reserves estimate before the end of March, potentially boosting its valuation.

(Reporting by Rosalba O'Brien; Editing by Hans Peters)