The workers, who were employed by a Turkish company, were sleeping in caravans at the site in the northern Shiite district of Sadr City when the gunmen arrived in black sports utility vehicles at dawn and took them away.

Police sources said the gunmen broke down the doors of the workers' caravans after disarming the guards.

Nurol Holding, which owns the construction firm, said no prior threat had been issued.

"People dressed in military uniforms broke down the door at 3am (midnight GMT) and abducted all these people," said Ugur Dogan, chief executive of Nurol Holding.

Tanju Bilgic, the Turkish Foreign Ministry spokesman, told the Associated Press that those kidnapped included 14 labourers, three engineers and an accountant.

Turkish Deputy Prime Minister Numan Kurtulmus insists the Turkish Government is in close contact with Iraq authorities, who are said to have no information on who was behind the kidnapping.

Having discarded months of caginess to launch air strikes against Islamic State (IS) in neighbouring Syria and open its bases to a United States-led coalition fighting the Sunni Muslim militants, diplomats have said Turkey could suffer retaliations.

Last year, 46 Turkish citizens were seized by IS militants in the northern Iraqi city of Mosul and were only released following more than three months in captivity.

Kurtulmus also said no contact had been made with a Turkish soldier who went missing late on Tuesday (September 1) during cross-border fire from territory controlled by the jihadist group IS in northern Syria, which left another solider dead.

Last month, the IS accused Turkish President Recep Tayyip Erdogan of "selling the country to crusaders".