Tighter security is seen at Penn Station after Gov. Andrew Cuomo announced an increase in police presence in New York City transportation hubs due to the threat of terrorism. (Credit: CBS 2)

NEW YORK (CBSNewYork/AP) — Iraq’s prime minister said Thursday that captive Islamic State militants told his intelligence agents of an alleged plot to attack subways in the United States and Paris, France.

Prime Minister Haidar al-Abadi said he was told of the purported plot by officials in Baghdad, and that it was the work of foreign fighters who had joined the Islamic State group in Iraq, including French and U.S. nationals. Al-Abadi’s assertion has not be independently confirmed by U.S. government intelligence.

Watch: Mayor de Blasio, Commissioner Bratton Address Terror Concerns

Asked if the attacks were imminent, he said, “I’m not sure.” Asked if the attacks had been thwarted, he said, “No, it has not been disrupted yet— this is a network.”

“Today, while I’m here I’m receiving accurate reports from Baghdad that there were arrests of a few elements and there were networks from inside Iraq to have attacks — on metros of Paris and U.S.,” al-Abadi said, speaking in English. “They are not Iraqis. Some of them are French, some of them are Americans. But they are in Iraq.”

Al-Abadi said the United States had been alerted. He declined to give the location in the U.S. where such an attack might occur.

He made the remarks at a meeting with journalists on the sidelines of a gathering of world leaders at the United Nations General Assembly.

A senior Obama administration official told The Associated Press no one in the U.S. government is aware of such a plot, adding that the claim was never brought up in meetings with Iraqi officials this week in New York. President Barack Obama met with al-Abadi Wednesday.

The administration official was not authorized to discuss the matter publicly by name and spoke on condition of anonymity.

A spokesperson for Mayor Bill de Blasio’s office released a statement saying that “the city takes any threat seriously.”

At a news conference outside the Union Square subway station Thursday afternoon, de Blasio worked to calm the nerves of New Yorkers after news of the alleged plot, saying city officials have found no specific threat.

“We are convinced that New Yorkers are safe,” he said. “We are convinced that people should go about our normal routine. Terrorists want us to live in fear. We refuse to live in fear.”

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The mayor also stressed the importance of the subway system’s “see something, say something” motto.

“The people of this city have an important role to play,” de Blasio said. “The phrase, ‘when you see something, say something’ is not an empty phrase. It is real.”

Joining de Blasio at the news conference, police Commissioner Bill Bratton echoed the mayor’s statements.

“At this time, the people of this city should feel very comfortable and secure moving through the subways,” he said.

Bratton said New Yorkers would see stepped-up security across the city and in all subway stations as a precaution.

As CBS 2’s Jessica Schneider reported, all Emergency Services officers are being deployed, additional bag checks are being performed inside subway stations and heavily-armed NYPD Hercules teams are being deployed across all five boroughs.

While many subway riders are anxious, not all of them are concerned.

“I’m a little leery getting on the subway, but it’s a way of life here,” one subway rider told CBS 2’s Andrea Grymes.