Baghdad ? U.S. authorities freed 500 Iraqi prisoners Thursday 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 latest release 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. U.S. 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 coincided with other signs of progress in regaining control of former extremist strongholds since the arrival of 30,000 additional U.S. troops earlier this year.

U.S. troop deaths and civilian casualties have dropped in recent months. U.S. forces, meanwhile, have made important alliances with Sunni clan leaders to battle extremists such as al-Qaida in Iraq.

But Sunni leaders also complain members of their sect make up the vast majority in both U.S. and Iraqi custody.

Flanked by U.S. soldiers, Prime Minister Nouri al-Maliki addressed the detainees, many wearing identical plaid shirts. “Dear brothers, let’s cooperate to shut down these prisons and write a new page of laws with the power of justice,” al-Maliki told the men, who sat in rows of white plastic chairs under the Baghdad sun.

The backgrounds of the prisoners, including any suspected militant links, were not announced. The military issued a news release saying only that the detainees are “no longer an imperative threat to Iraqi/coalition forces and the security of Iraq.”