Genk have confirmed that a £3.1m bid from Middlesbrough for striker Jelle Vossen has been rejected.

Middlesbrough head coach Aitor Karanka is believed to have been targeting the 25-year-old for a number of months, but Genk chairman Herbert Houben insists that the Championship side are still short of their valuation.

"We want to fulfil our promise, but that does not mean we have to let him go for anything," Houben, who has informed Vossen that the club are willing to sell him this summer, told Het Nieuwsblad.

"There was a more lucrative offer from Russia [in January] at which point we agreed with Jelle to cooperate, but only at that level or similar, but there has been no bid like that yet.

"I firmly believe in the next few weeks and months, better offers will come."

Vossen scored 12 goals in the Belgian Pro League last season.