BAGHDAD -- An Iraqi police commander and a Western security official in Baghdad have named two powerful Shiite militias as top suspects in the abduction of three Americans last weekend in a southern neighborhood of the Iraqi capital.

They say one of the two militias -- Asaib Ahl al-Haq and Saraya al-Salam -- were likely behind the attack.

The police commander says "nobody can do anything in that neighborhood without the approval of those militias." The Western security official confirmed that intelligence assessments had narrowed down the suspects to those the two groups.

Both officials spoke on condition of anonymity because they are not authorized to talk to reporters.

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The U.S. Embassy in Baghdad has confirmed that several Americans are missing and says they are working with Iraqi authorities to locate them.

The abduction over the weekend was just the latest in a series of brazen high-profile kidnappings undermining confidence in the Iraqi government's ability to control state-sanctioned Shiite militias that have grown in strength as Iraqi security forces battle the Islamic State of Iraq and Syria (ISIS).

Witnesses said men in uniform carried out the kidnapping in broad daylight Saturday, 100 yards from a police station in the Baghdad neighbourhood of Dora.

A map of Baghdad, Iraq. Google Maps

In spite of the information to the contrary, Iraq's Prime Minister on Thursday insisted there was still no evidence to prove the missing men and one woman had been abducted.

"We don't know that they were kidnapped," he told reporters on the sidelines of the Davos economic summit in Switzerland. "They just went missing."

Abadi also cast doubt on any possible link between their disappearnace and the goverment in Tehran, saying he would "doubt it very much."

Dora is a mixed neighborhood that is home to both Shiites and Sunnis. However, the victims were then taken to Sadr City, a vast and densely populated Shiite district to the east, and there "all communication ceased," an Iraqi intelligence official told The Associated Press. The official spoke on condition of anonymity because he was not authorized to speak to reporters.

A State Department source told CBS News that the U.S. embassy received threat information last week that an Iranian-backed Shiite militia group wanted to seize an American or an American contractor.

Officials in Washington had hoped the Iranian government would tell the militia group to hold off because of all the negotiations surrounding the prisoner swap that saw the release of five Americans. The State Department source said the fear was that one of the groups might have "gone off the reservation."

A similar scene unfolded in September, when masked men in military uniforms abducted 18 Turkish workers from a construction site in a Shiite neighborhood. A hostage video later showed the men standing before a banner that read "Death Squads" and "Oh, Hussein," a Shiite religious slogan. The workers were released later that month.