There is no evidence of any new, specific threat to New York City's subway system, according to intelligence sources asked about potential developments after the Associated Press reported the Iraqi prime minister said his country's intelligence operation uncovered a plot for an imminent attack.

The mayor and the police commissioner also said in a news conference they assessed the prime minister's "vague" statements and found no credible threat. 

The Associated Press reported Prime Minister Haider al-Abadi said Thursday he was told of the alleged plot by Baghdad, and that it was the work of ISIS in Iraq. Asked if an attack was imminent, he said, "I'm not sure," according to the AP. He also said the United States had been alerted about the threat, according to the AP, but security officials tell NBC 4 New York that is not true.

No overseas partner told U.S. law enforcement of any new or specific such threat, a senior security official said, nor have authorities at the FBI, NYPD, Port Authority or MTA uncovered evidence indicative of any new, specific plot targeting the city's transportation system

"The first we heard of this threat is when the press began reporting it," the official said.

At a briefing at the Union Square subway station, Mayor Bill de Blasio and Police Commissioner Bill Bratton said they assessed the prime minister's statements and found "no credible threat," but police will remain "ever vigilant," said de Blasio. 

The city has already been on high alert due to the United Nations General Assembly and the Jewish high holidays, Bratton said, and that heightened security level "can be very quickly enhanced."

De Blasio and Bratton assured New Yorkers that they should feel "very comfortable and very secure riding the subways," according to Bratton. 

The police commissioner added that he and the mayor had just taken the subway to Union Square with Yankees fans on their way to Yankee Stadium to celebrate Derek Jeter's last home game there.

Nevertheless, the mayor urged residents to remain as vigilant as always.

"Law enforcement depends on everyday citizens to alert us to any potential threat," he said.  

Al-Abadi made the initial remarks in a media roundtable. In expanded remarks to NBC News later, an Iraqi official clarified the prime minister's statements, saying the Paris public transit system was a target, but that no specific target in the United States had been revealed.  

A federal security official said the prime minister's comments "took us security officials by surprise." Another senior official said, "We don't know what he is talking about."

An internal Homeland Security bulletin to law enforcement agencies said the department's intelligence unit has been working with multiple intelligence community partners to try to identify the kind of threat reports that al-Abadi referred to. 

But "no similar threat reporting can be located," stated the bulletin, obtained by NBC News. "Nor is it clear who, or what agencies in the United States Government were alerted." 

Authorities are looking into the source of his information and comparing it against past "open source" intelligence from about a month ago alleging a possible threat against the metropolitan area's commuter rail system, but they stress they have found no new threat to local infrastructure.

Nothing about the prime minister's statement has been validated and no one knows where his information came from, one New York security official said.

The NYPD said in a statement it was aware of the prime minister's statements and was in close contact with the federal law enforcement agencies "as we assess this particular threat stream."

"New York City normally operates at a heightened level of security and we adjust that posture daily based on our evaluation of information as we receive it," the statement said.

Officials have stepped up security across the tri-state area in response to the ISIS threat overseas in weeks out of an abundance of precaution.

Last week, a post on an ISIS message board titled “To the Lone Wolves in America: How to Make a Bomb in Your Kitchen, to Create Scenes of Horror in Tourist Spots and Other Targets” encouraged readers to attack sites throughout the country, including Times Square.

Earlier this week, the extremist group purportedly released a new audio that warned Americans "you will not feel secure even in your bedrooms."

On Wednesday, Govs. Cuomo and Christie announced a bi-state agreement to coordinate intelligence-gathering and share information as part of a plan to step up security in the wake of the threat overseas. A senior security official told NBC 4 New York if tri-state area residents notice a ramping up of security on trains Thursday, it's because of that agreement and the general threat environment, not because of the remarks by Iraq's prime minister.

The bi-state agreement to substantially increase security at transportation hubs and critical infrastructure in the metropolitan area is effective immediately. Over the next 100 days, law enforcement and military personnel will join forces within the metropolitan area to engage in counterterrorism operations by increasing visibility, inspections and surveillance on and at trains and train stations, airports, landmarks, and bridges and tunnels, according to the plan.

The two states will also participate in a joint emergency exercise in the coming months and continue to evaluate methods for increased intelligence and emergency coordination.

Follow Jonathan Dienst on Twitter @jonathan4NY