FRANKFURT, Feb 6 (Reuters) - Investment fund Primestone Capital has raised its stake in German research firm GfK to 5 percent from 3.21 percent, GfK said in a statement on Monday.
The regulatory statement comes only days ahead of the end of the tender period for the 43.50 euro per share offer from KKR , which ends on Feb. 10.
The offer values the research firm, whose majority shareholder GfK Verein will hold on to its 56.46 percent stake, at around 1.59 billion euros ($1.71 billion).
Last week, personal computer firm founder Michael Dell disclosed a 6.45 percent stake in the company.
GfK shares were down 0.3 percent at 43.61 euros by 1300 GMT, but still above KKR's offer price of 43.50 euros. ($1 = 0.9324 euros) (Reporting by Harro ten Wolde; Editing by Georgina Prodhan)