Cities across the world have ramped up security measures in anticipation of the New Year's Eve celebrations on Thursday.

According to Reuters, U.S. officials are closely monitoring overseas investigations into alleged New Year's terror plots by Islamic State militants and sympathizers.

Officials have noted arrests made in Turkey, Belgium and Indonesia, in connection with potential terrorist attacks by ISIS.

"Security services are rightly worried that Islamic State and al Qaeda will try to direct or inspire an attack early in the new year to follow up the Paris operation. The plan for an attack on Brussels' iconic grand market would be just such a spectacular assault," said former senior CIA expert Bruce Riedel, who in the past has also served as a Middle East policy advisor for President Barack Obama.

EFE reports Brussels Mayor Yvan Mayeur announced Wednesday that the annual fireworks celebrations would be cancelled. The decision was made following a Tuesday operation, in which an alleged terror plot targeting "several emblematic sites" on New Year's Eve was foiled by Belgian security forces.

Mayeur said that the risk was "significant," but encouraged people to continue to celebrate the New Year at other venues.

Authorities in Turkey also arrested two suspects on Wednesday, in apparent connection to a possible New Year's Eve attack in Ankara.

Officials at the Department of Homeland Security and other agencies assured that there were no credible threats made against U.S. targets.

The New York Police also said that there were no known New Year's Eve threats made against the city but nevertheless, emphasized that security would be at its highest levels since the Sept. 11 attacks in 2001.

"There will be a tremendous number of officers that you will see, there will be many officers you won't see," said New York Mayor Bill de Blasio at a press conference this week, according to the Washington Post.

The U.S. Federal Bureau of Investigation also called for the public to remain alert.

"While the FBI and Department of Homeland Security are not aware of any specific, credible threats to the homeland, we continue to take proactive steps to ensure personnel and resources are in place to ensure the safety and security of our communities," said the FBI in a statement.