UPDATE 1-WPP asks TNS shareholders to press board for talks

(Adds reaction, share price)

By Kate Holton

LONDON, May 6 (Reuters) - Advertising group WPP Plc (WPP.L: Quote, Profile, Research) has urged Taylor Nelson Sofres (TNS.L: Quote, Profile, Research) to engage in talks over a possible offer, sending shares in the market research firm up over 13 percent as investors eyed a looming bid battle.

British-based Taylor Nelson (TNS) said on Sunday it had rejected a 230 pence a share, or 950 million pound ($1.9 billion), offer from WPP, saying it preferred to press ahead with talks on a nil-premium merger with Germany's Gfk (GFKG.DE: Quote, Profile, Research).

Analysts interpreted the WPP move as opportunistic, with the world's second largest advertising company looking to acquire the smaller market research firm before it becomes a larger entity with a blocking shareholder.

But they also thought WPP could return with a higher offer.

"We are surprised and disappointed that the board of TNS has rejected our offer proposal within 24 hours of receipt," WPP Chief Executive Martin Sorrell said in a statement.

"While we continue to review our position, we encourage TNS shareholders to urge their board to engage with us rather than simply persisting on an exclusive basis with a 'nil premium merger' arrangement with GfK."

TNS shares were up 11.6 percent to 240 pence at 1005 GMT on Tuesday.