The row between Borussia Dortmund and Bayern Munich over Marco Reus flared again when BVB sporting director Michael Zorc said he would be delighted if Bayern CEO Karl-Heinz Rummenigge "could keep his mouth shut for once."
Bayern are interested in signing Germany international attacker Reus, whose contract includes a release clause that would enable him to join another club next summer.
The 25-year-old is under contract until 2016, but Rummenigge said ahead of Bayern's match against MLS All-Stars last week that the clause -- previously reported to have been 35 million euros -- had in fact been set at 25 million euros.
He again hinted at his club's interest in a deal for Reus and added that Bundesliga runners-up Dortmund might find it "difficult" to remove the clause from his contract.
That drew an angry response from Borussia chief Hans-Joachim Watzke, who said: "We are sure that it is quite clear to anybody interested in football what intentions lie behind such remarks." Watzke has previously insisted that Reus wants to stay.
Zorc hit out strongly in an interview with Sport 1 on Friday, saying there was a "three-day rhythm" of Bayern comments about Dortmund players, but Munich sporting executive Matthias Sammer told the same channel on Saturday: "We will not allow anyone to forbid us to speak."
The two clubs meet in the German Supercup at Dortmund's Westfalen Stadium on Wednesday, with the ongoing row stoking up interest in the clash.
The relationship between the two clubs -- already frosty following the transfers of Mario Gotze and Robert Lewandowski to Munich -- has worsened, and Watzke told kicker he would not attend the prematch dinner because of the "profound disharmony."
Rummenigge told Bayern's official website: "As always when Bayern and Dortmund clash, there is a certain explosive nature to it. We'll go there and try and give a good performance."
Meanwhile, Watzke has extended his contract with Dortmund until 2019, a club statement said.
His existing deal had been due to run out in 2016, and president Reinhard Rauball said: "He was an architect of the recent past of the BVB, is a builder of the present and will oversee, sustainably, the development of this great club."