The 21-year-old had already agreed terms with the Bundesliga club and passed a medical in the Westphalian city, but Poznan refused Dortmund's initial bid.

Protracted negotiations have finally reached a compromise, allowing the Polish forward to join Dortmund for pre-season training on July 4 having signed a four-year contract.

"We are pleased that Robert will be playing in our attack next season," commented Dortmund's director of sport Michael Zorc on his club's website.

"We are glad that, after hard but fair negotiations, we were able to reach an agreement."

Lewandowski was the top goalscorer in the Polish league last season when he won the title with Poznan.

He has made a total of 20 international appearances, scoring six goals.