The head of one of Iraq's strongest Iranian-backed Shia militias, Asaib Ahl al-Haq, denounced on Thursday the kidnapping of 18 Turkish workers but condemned Turkey as the country's biggest enemy.

The captives appeared in a video days after their abduction that featured Shia Muslim slogans and threatened to attack Turkish interests in Iraq if its demands were not met, reported Reuters.

Eighteen Turkish workers were kidnapped by an armed group in Baghdad earlier this month.

No group has claimed responsibility for the kidnapping and it is as yet unclear if the gunmen belong to an established group.

Iraqi security forces investigating the abduction raided the Baghdad headquarters of another Iranian-backed Shia militia Kataib Hezbollah, but without result, reported Reuters.

Baghdad has struggled to control Shia militias, seen as critical weapons against IS, or control criminal gangs involved in contract killings, kidnappings and extortions.

Asaib Ahl al-Haq leader Qais al-Khazali said the group was not behind the kidnapping, but he reiterated demands made of Ankara in the ransom video. Khazali called on Turkey to stop the passage of militants into Iraq, cut the flow of oil from Iraq's semi-autonomous Kurdistan region, and order the lifting of a siege on two Shia villages in northwest Syria.

"The Turks - the Turkish intelligence - are the ones who ease the entrance of large numbers of Daesh (Islamic State), including suicide bombers, from Turkey to Syria and from Syria to Iraq, killing Iraqis by hundreds and thousands," Reuters reported Khazali as saying in an interview with Iraqi state TV.

Thousands of foreign fighters have crossed through Turkey to join IS over the past few years.

The Turkish government's critics and opposition newspapers have accused Turkey of turning a blind eye, while Ankara has repeatedly denied those accusations.

"The biggest enemy of Iraq now is Turkey, and this enemy is the first and one of the biggest benefactors of Iraq's riches," Reuters reported Khazali as saying, while apparently referring to oil smuggled by IS or sold by the Kurdistan Regional Government via a pipeline to the Turkish port of Ceyhan.

The Shia militia leader said Turkey played a more negative role in the region than Saudi Arabia or Qatar, Sunni Gulf Arab states which Iraqi Shia politicians have accused of funding IS insurgents, allegations denied by both countries.

Two of the 18 Turkish hostages were released on Tuesday in the southern city of Basra, but the others remain missing.

Asaib Ahl al-Haq split from Moqtada al-Sadr’s Jaish al-Mahdi in 2006 and has since conducted thousands of lethal attacks against US and Iraqi forces, according to a report published by the Institute for the Study of War in 2012.

The group, which has close connections to Iran, has been provided organised training by a Lebanese Hezbollah operative named Ali Mussa Daqduq, according to the report.