(AP) -- New York's top government officials have taken to the nation's largest subway system following the disclosure of an alleged terrorist attack on trains in U.S. cities.

Gov. Andrew Cuomo and Metropolitan Transportation Authority Chairman Tom Prendergast rode a train from the World Trade Center to Penn Station in Manhattan Thursday afternoon.

Cuomo said there was no specific, credible threat to New York City subways.

Mayor Bill de Blasio and Police Commissioner William Bratton also took the train Thursday. They say transit security has been heightened as a precaution.

The officials took to the rails to urge calm after Iraq's prime minister said captive Islamic State militants told intelligence agents of an alleged plot to attack subways in the United States and Paris.

About 5.5 million daily passengers take city subways.