Eleven Iraqis detained at a US prison in southern Iraq escaped on Saturday, but 10 were quickly recaptured, US officials said.
The men broke out at around 1:30am after cutting a man-sized hole in the perimeter fence of Camp Bucca, a US-run facility near the town of Umm Qasr, where around 6,500 detainees are held.
The jail break is believed to be the first from a US prison in Iraq.
"We discovered the hole and after conducting a head count found that 11 detainees had escaped," Lieutenant Adam Rondeau said.
Iraqi security forces searched for the men at daybreak and soon recaptured 10 of them, Rondeau said. US and Iraqi authorities are searching for the 11th.
The breakout follows the discovery last month of several tunnels at Camp Bucca, one of which was 600 feet (about 200 metres) long and reached out of the camp.
The tunnels were discovered before anyone could escape.
None of those who escaped was a high-value detainee, Lieutenant Rondeau said. He gave no details on how long they had been held or the charges against them.
There are around 10,000 people in US custody in Iraq. Most are being held on suspicion of aiding the country's 2-year-old insurgency.
Lieutenant Rondeau said an investigation had been launched. It was not clear if those recaptured would be punished.