German carmaker Audi's cash pile grew over the first half of the year, and now accounts for nearly 80 percent of parent Volkswagen's war chest.

The premium carmaker said on Friday its net liquidity rose to more than 9.7 billion euros ($13.7 billion) at the end of June from 9.3 billion euros at the end of December. VW had said on Thursday its automotive net liquidity stood at 12.3 billion.

Volkswagen will likely use part of its cash to buy sports car maker Porsche AG.

Last week, Porsche's two top executives left the company, removing the last big hurdle to a deal that would see Qatar become VW's third largest shareholder with an estimated 17 percent, while eventually bringing the iconic maker of 911 Carreras into the VW group as its tenth brand.

Audi high-end sportscar unit Lamborghini's Chief Executive Stephan Winkelmann told Reuters that he was not concerned about the prospect of Porsche joining the ranks.

We have always cooperated very closely within the company, he said in an interview , adding that each product had a defined market position.

Audi on Friday affirmed its target of posting a significant operating profit in 2009, though it said there were still several challenges to be faced in the second half of the year.

(Reporting by Maria Sheahan)