Primestone called on Wednesday for the two companies to merge after it built up a more than 5 percent stake in both firms.

"Nilfisk's strategy continues to be to simplify its business and to grow organically and through M&A," the Danish company, which was spun off from cable maker NKT, said in a statement.

Nilfisk shares were up 4.2 percent at 332.30 Danish crowns as of 1524 GMT. They have risen 11.8 percent since Primestone's statement on Wednesday.

(Reporting by Thyagaraju Adinarayan in Gdynia; Editing by Susan Fenton)

Stocks treated in this article : Tennant Company, NKT A/S, Nilfisk Holding A/S