** Shares in ad firm WPP up as much as 4.1% at 903p

** Shares at highest level since May 2023, stock top pct gainer on FTSE 100 index

** Wall Street Journal reports ad firms Omnicom and Interpublic Group near merger

** Analysts at JP Morgan say merger could improve market structure and reduce competition for peers including WPP

** A deal may be subject to regulatory concessions and enforced disposals in some channels and geographies which would create opportunities for WPP - JPM adds

** The merger, if successful, will however topple WPP as the world's largest ad agency, according to WSJ

** WPP up ~18% so far this year

(Reporting by Prerna Bedi in Bengaluru)

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