BERLIN: Volkswagen AG has called off the next round of talks over a planned integration with sports car maker Porsche SE, saying the atmosphere is not right for constructive discussions, officials said Sunday.

The Wolfsburg-based car maker had pulled out the next round of talks at the working group level that were scheduled for Monday, VW spokeswoman Christine Ritz told The Associated Press.

VW chairman Ferdinand Piech and members of the Porsche family - controlling shareholders of Porsche Automobil Holding SE - will come together as planned at a meeting of Porsche's supervisory board Monday, she said.

Porsche declined to comment.

Earlier this month, Piech and the Porsche families agreed on a plan to integrate the Porsche car-manufacturing group with Volkswagen, under which the independence of the 10 brands of both companies would be ensured.

But Piech threw the plan into question Tuesday, by saying Porsche must reduce its debt before an integration could be possible, referring to the euro9 billion ($12.22 billion) in net debt Porsche took on as it brought its stake in Volkswagen up to 51 percent last year.

"Constructive negotiations" were not possible in the "current environment" and urged Porsche to clarify exactly how it envisions the integration process moving forward, Gunnar Kilian, spokesman for the head of Volkswagen's works council, Bernd Osterloh, told The Associated Press.

"Before we can proceed, Porsche needs to clarify exactly how they want to proceed in the event of a fusion. In particular, this needs to be discussed with our colleagues at Porsche," Kilian wrote in an e-mail.

"Everyone at Volkswagen - from the supervisory board to the executive board to the works council - is open for a solution. But Porsche needs to make it clear internally what they hope to achieve."