US authorities freed 500 Iraqi prisoners in an ongoing push to empty American jails of detainees no longer deemed a threat. But the military says it's still holding 25,800 Iraqis waiting to face charges or be given freedom. The releases on Thursday provided only small relief to a detention system strained to the limit by about 17,000 new suspects captured this year in campaigns to secure Baghdad and its surrounding belts, the military said. US officials worry the overcrowded detention camps are sapping resources and will overwhelm Iraq's struggling justice system. The periodic releases are seen as both a symbolic gesture to highlight increased security and a needed safety valve. About 6,300 detainees have been released since January. The ceremony - held behind concrete blast walls at Camp Victory, a sprawling US base that contains several of Saddam Hussein's former palaces - coincided with other signs of progress in regaining control of former extremist strongholds since the arrival of 30,000 additional US troops earlier this year.