New Year’s Eve is unfolding around the world in an atmosphere of heightened security, after recent terrorist attacks in Paris and San Bernardino, Calif., associated with or inspired by the Islamic State. The authorities in Turkey and Belgium announced this week that they had disrupted terrorist plots aimed at popular destinations in the capitals.

New York City

The Police Department will deploy 6,000 officers around Times Square for the annual ball drop at midnight — about 600 to 800 more than usual, according to Police Commissioner William J. Bratton. “The public should expect to see, not only in the Times Square area, but literally throughout the city, particularly at the special venues, a very significantly enhanced police presence,” Mr. Bratton said on Tuesday at a news conference with Mayor Bill de Blasio.

Paris

With the Nov. 13 terrorist attacks in mind, the authorities in Paris have opted to mark the holiday in “an atmosphere of sobriety,” France 24 reported. A fireworks display on the Champs-Élysées has been abandoned in favor of a video show. Security will be tight, with 11,000 soldiers, police officers and emergency workers deployed across the city, 2,000 more than last year, the news channel said on its website.