June 13 (Reuters) - Britain's Spectris SXS.L said on Friday it has rejected a takeover proposal from private equity firm KKR, days after the scientific instruments maker backed a possible competing $5 billion dollar bid from Advent.

Spectris did not provide details on KKR'S proposal, first reported by the Wall Street Journal.

(Reporting by Prerna Bedi in Bengaluru; Editing by Vijay Kishore)

((Prerna.Bedi@thomsonreuters.com; +91 98052 24616;))