Milan's Arbitral Tribunal has judged that the 2013 sale of RCS' headquarters to Blackstone Group was valid but found that the purchaser's behaviour may entitle the Italian publisher to compensatory damages, RCS said late on Tuesday.

In relation to potential damages, RCS said that the arbitral court had ordered two expert witnesses to report separately on the financial situation of RCS in 2013 and on the market value of the property at the time.

A spokesman for Blackstone on Wednesday said that the only decision the court had taken was on the validity of the sale.

"There was absolutely no decision or assessment about any right to damages for RCS," he said in an emailed statement.

Shares in RCS, the publisher of Corriere della Sera daily, rose as much as 16.6% on Wednesday, before trimming gains after Blackstone's statement to stand 7.9% higher by 1409 GMT.

The case centres on the ownership of RCS's historic headquarters in central Milan, which Blackstone bought for 120 million euros.

After a change at the helm, RCS launched proceedings in Milan in 2018 to nullify the sale, saying Blackstone had paid too low a price because RCS was facing financial difficulties.

Blackstone in turn has accused RCS of falsely claiming that it still owns the building and of improperly blocking its sale to Germany's Allianz SE.

The U.S. investment firm filed two lawsuits in New York which were put on hold last year pending the outcome of the arbitration in Italy.

A Blackstone representative said late on Tuesday the company was "pleased that in this ruling, the arbitrators have dismissed the overwhelming majority of RCS' claims", adding Blackstone would continue to seek "compensation for the meaningful and growing damages caused by RCS."

RCS said the court's decision was partial and non-definitive and the arbitration proceeding continued.

(Reporting by Claudia Cristoferi and Valentina Za; Editing by Gavin Jones, Matthew Lewis, Kirsten Donovan)