Borussia Dortmund has completed the signing of striker Sebastien Haller from Dutch side Ajax Amsterdam on a four-year contract, the Bundesliga club said on Wednesday.

British and German media reported that Dortmund paid an initial fee of 31 million euros ($31.55 million) for the Ivory Coast international, who joined Ajax from West Ham United on a four-and-half year deal in January 2021.

"We're very pleased to have been able to sign Sebastien Haller - a seasoned centre-forward who has recently caused a sensation in the Champions League," said Dortmund's sporting director Sebastian Kehl.

"The overall package is very promising. Sebastien possesses a strong physical presence and he is physically very resilient."

The 28-year-old netted 34 times in 43 appearances across competitions for Ajax last season, helping it to the Eredivisie title. He comes in as a replacement for Erling Haaland, who moved to Manchester City earlier in the close season.

Dortmund, which replaced manager Marco Rose with Edin Terzic in May, finished second last season, eight points behind champion Bayern Munich.

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Earlier, Belgium attacking midfielder Axel Witsel joined La Liga club Atletico Madrid on a free transfer after leaving Dortmund at the end of his contract in June.

Witsel, who has signed a one-year deal with Atletico, made 145 appearances in all competitions for Dortmund after joining them from Chinese club Tianjin Tianhai in 2018.

The 33-year-old has played 124 times for Belgium and was part of the team that finished third at the World Cup in 2018.