Baghdad (AFP) - US and Iraqi authorities were searching on Monday for three Americans who were kidnapped in Baghdad, the latest group of foreign nationals abducted in recent months.

The three US nationals were kidnapped from a "suspicious apartment", a security official said, using language implying the location was a brothel.

Kidnappers have recently seized Qataris and Turks, but it has been years since Americans were abducted, and Iraqis have suffered the most from kidnappers seeking ransoms or to settle scores.

The Islamic State group, which overran large areas in 2014, has abducted thousands of people and carried out a slew of executions, while Shiite paramilitary forces opposed to the jihadists have also carried out kidnappings and killings.

Iraqi parliament speaker Salim al-Juburi condemned the rise in "cases of foreigners being kidnapped in Iraq," saying it would harm the country's relations with other states.

"The kidnapping of the American citizens yesterday, and before them the Qatari hunters, whose fate is still unknown, without a doubt indicates the increasing work of organised gangs in Iraq," Juburi said in a statement.

US State Department spokesman John Kirby said the day before that: "We are aware of reports that American citizens are missing in Iraq."

"We are working with the full cooperation of the Iraqi authorities to locate and recover the individuals," Kirby added, without providing details about their number or the circumstances of their disappearance.

An Iraqi police colonel said on condition of anonymity that three Americans and an Iraqi translator were kidnapped in southern Baghdad.

The colonel said on Monday that the search was at this point mainly an intelligence effort.

The officer earlier said that according to information he had received, the kidnappers were militiamen wearing military uniforms.

"We don't know what their work is," the colonel said of the kidnapped Americans.

Iraq turned to paramilitary forces dominated by Iran-backed Shiite militias to help combat the Islamic State jihadist group, which overran large parts of the country in 2014.

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- Qataris and Turks kidnapped -

These groups, which fall under an umbrella organisation known as the Hashed al-Shaabi, or Popular Mobilisation units, have played a key role in the fight against the jihadists.

But they have also been accused of abuses including summary executions, kidnappings and destruction of property.

The US is leading a coalition of countries that have bombed thousands of IS targets in Iraq and Syria and which are providing training to Baghdad's forces.

Washington has also dispatched special forces to Iraq to carry out raids against the jihadists.

Both American forces and Shiite paramilitaries are battling IS, but relations between the two sides have been tense, especially due to fighting between them in the years after the 2003 US-led invasion of Iraq.

IS also has ample motive to target Americans, but while it is able to carry out bombings in Baghdad, it does not have a major presence in the city.

Dozens of foreign nationals have been kidnapped in two incidents during the past five months, but kidnappers also frequently target Iraqis.

Last month, gunmen kidnapped more than two dozen Qataris who had come to southern Iraq to hunt.

Their whereabouts are still unknown, as are the identities of their kidnappers. But Shiite militia groups have a major presence in southern Iraq, while IS does not.

The kidnapping of the Qataris came a little over three months after gunmen seized 18 Turks in Baghdad. They were later released unharmed.

The kidnapping of the Turks was claimed by an organisation that presented itself as a Shiite group called "Furaq al-Mawt", or "Death Squads", in a video claiming the abductions.

Iraqi security forces clashed with fighters from the powerful Ketaeb Hezbollah militia during the search for the kidnapped Turks.

It has been years since an American was kidnapped in Iraq.

Issa T. Salomi, an American of Iraqi origins, went missing in Baghdad in January 2010 and was later freed by Asaib Ahl al-Haq, a powerful Shiite group that is now one of the leading forces in the Hashed al-Shaabi.