UEFA is withholding Champions League and Europa League prize money from six clubs over unpaid debts.

UEFA said Friday the clubs are Astra Ploiesti, Metalurg Donetsk, Hajduk Split, HSK Zrinjski, Skonto Riga and Trabzonspor. A further 25 clubs, which UEFA did not name, must also provide further information about apparent financial problems.

All 31 have been given a Sept. 30 deadline.

The new cases involve ''overdue payables,'' including late payments of transfer fees, wages and social taxes.

Last season, Champions League quarterfinalist Malaga failed to meet repeated UEFA deadlines and was banned from this season's Europa League. Malaga had earned the entry by finishing sixth in the Spanish standings. The latest provisional sanctions ''remain in force until all identified balances have been settled in full,'' or its club finance panel gives final verdicts, UEFA said.

UEFA monitors the accounts of hundreds of clubs qualifying to play in its European competitions, and noted a positive trend as its new ''Financial Fair Play'' rules take greater effect.

UEFA figures released Friday showed that clubs owed 9 million euros ($12.2 million) in overdue payments by June 2013, compared to 57 million euros (now $77 million) two years earlier.