Borussia Dortmund on Saturday confirmed the signing of South Korea international left-back Park Joo-ho from Bundesliga rivals Mainz for a reported 3.5 million euros ($3.9m) on a contract until 2018.

"As a left-back, Park Joo-ho is the ideal addition to our squad," said Dortmund's director of sport Michael Zorc.

The 28-year-old has made 26 appearances for Korea and was a late call-up to their 2014 World Cup squad.

Park will rival Germany international Marcel Schmelzer for the left-back berth.

He has played in the German league since joining Mainz in July 2013 from FC Basel, where he twice won the Swiss league title, and has played in 44 Bundesliga matches.

Park leaves Mainz with the Rheinland club's blessing and they have already lined up Gaetan Bussmann from French side FC Metz as Park's replacement.

"The years together with Park Joo-ho will stay with us as very good memories," said Mainz's team manager Christian Heidel

"Park approached us with the expressed desire to switch to Borussia Dortmund and once we had reached an agreement with them, we didn't want to stand in his way."

Dortmund host Hertha Berlin on Sunday in the Bundesliga chasing their eighth straight win at the start of the season under new coach Thomas Tuchel and have qualified for the Europa League's group stages.