The following is via ABC News:

Cities across the U.S. are heightening security after a series of deadly incidents abroad, including an attack in Berlin, where a truck plowed into a crowd at a busy Christmas market.

Additional police officers are being deployed in New York and Chicago, with emphasis on crowded public areas and holiday gatherings. Both cities cautioned that the increased presence of law enforcement was a preventive measure and that no specific threats were received.

“The NYPD is monitoring the events in Germany and around the world today,” the New York Police Department said in a statement Monday. “The department has moved highly trained teams, including the critical response command, to high-profile locations around New York City.”

In a statement, the Chicago Police Department said it is “adding police resources to Daley Plaza, including additional foot and bike patrols and specialized units.” Daley Plaza in the Loop, a busy commercial neighborhood in the city, hosts a holiday marketplace as well.

In Berlin on Monday evening, 11 people were killed after a truck plowed through Breitscheidplatz, a public square hosting a Christmas market. A 12th victim was discovered dead in the cabin of the truck, and at least 48 others were injured. German Chancellor Angela Merkel later said, “We must assume that it was a terrorist attack.”

The incident capped a deadly day, as earlier on Monday, the Russian ambassador to Turkey was assassinated at a museum in the Turkish capital, Ankara, by a man who appeared to be protesting Russia’s involvement in the Syrian civil war. Also on Monday, three people were wounded after a gunman opened fire at an Islamic center in Zurich, Switzerland.

In a memo distributed last month, U.S. intelligence officials noted the possibility of holiday celebrations being targeted by terrorist organizations.

A joint intelligence bulletin distributed by the FBI and the Department of Homeland Security on Nov. 18 read, “Law enforcement, military and security personnel” are reminded “to remain vigilant and aware of upcoming public and private events this holiday season and during the presidential inauguration.”

“We continue to monitor threats with an unspecified attack date emanating from foreign terrorist organizations … in the event that these groups advance their plotting efforts in the near term to coincide with the holidays,” read the bulletin. “Based on historical precedence during past holiday seasons and presidential transition periods, we expect to see an increase in threat reporting between now and the end of January 2017.”

In addition to the NYPD, police departments in Chicago, Boston and Washington, D.C., indicated that they would continue to monitor events in Berlin and elsewhere around the world as they continue to prepare for possible residual effects in those cities.

The NYPD said it “will look to learn more about what occurred to inform operations, deployments and training of officers.”

(ABC News)