More than 30 Iraqis are still missing after a mass kidnapping of workers at two government factories on Wednesday.
Officials at the ministry of industry say a total of 64 employees were kidnapped, but 30 of them - mainly women - were later released.
The fate of the others is unknown, but an official said every effort was being made to secure their release.
Also on Wednesday, the US military said four marines had been killed in "enemy action" in western Iraq.
Three of the marines were killed when their vehicle hit a roadside bomb in Anbar province on Tuesday.
The fourth died after coming under fire during "security operations" in the same province, a statement said.
More than 2,500 US troops have died in Iraq since the 2003 invasion that toppled Saddam Hussein, most of them in attacks by anti-US insurgents.
Initial reports about Wednesday's mass kidnapping said at least 80 people were seized when a large group of armed men ambushed the workers as they left the factories.
As well women being released, there are reports that the kidnappers inspected workers' ID cards to check if they were Sunni or Shia Muslims, suggesting a sectarian motive.
Two people who tried to escape were shot dead by their abductors, eyewitnesses and officials say.
A Shia Muslim quoted by Associated Press said he had been set free after showing the kidnappers a forged ID card listing him as a Sunni.
"One of the gunmen told us to stand in one line and then asked the Sunnis to get out of the line. That's what I did. They asked me to prove that I am a Sunni, so I showed the forged ID and three others did the same," the man is quoted as saying.
The two factories at Taji just north of Baghdad, called Hattin and Nasr, were involved in military production under Saddam Hussein's government.
The factories remain state-owned, but have since been converted to civilian use.
About 4,000 people work at the Taji industrial complex.
The incident was the latest in a series of mass abductions of workers in Iraq, many of whom have been ransomed or killed.