Four Iraqi detainees with links to al-Qaida have escaped from the U.S.-controlled part of Iraqi detention center in Baghdad, an Iraqi police source said on Thursday.

"Four detainees escaped from the U.S. custody in al-Karkh prison, formerly called Camp Cropper. The U.S. military informed the Iraqi side on Thursday morning," the source told Xinhua on condition of anonymity.

It was not immediately clear when and how the detainees escaped, the source said.

Iraqi security forces surrounded the nearby Jihad neighborhood in southwestern Baghdad early in the morning and carried out search operation looking for the fugitives who possibly hide there, the source added.

The U.S. military confirmed the incident but did not give details.

On July 22, four al-Qaida prisoners, including the finance and interior ministers of the self-styled Islamic State of Iraq (ISI), escaped from the prison nearly one week after the detention has been transferred to Iraqi authorities.

On July 15, the U.S. military handed over control of the last detention center in Iraq to the Iraqis, including hundreds of prisoners, but kept some 200 detainees in the U.S. custody at a separate part of the facility which the Iraqis changed its name to al-Karkh prison.

Camp Cropper is a tented internment facility for security detainees near Baghdad International Airport. The facility was initially established as a high-value detention site run by U.S. army.

Later the site has been upgraded and its capacity increased from 163 to 2,000 detainees after the Abu Ghraib prison scandal in 2004 when dozens of pictures publicly circulated by the media showing Iraqi prisoners naked and humiliated by their American guards.