After a series of terrorist bombings killed at least 34 people in Brussels on Tuesday, major metropolises around the world, from New York to Budapest, responded immediately to the increased threat, sending security forces to landmarks, tourist spots, and transportation hubs. The heavily armed teams of police are a grim reminder that what happened in Brussels could happen anywhere. Here, a look at the international community on high alert.

New York City police officers patrol the Times Square subway station in New York City on March 22. | (EPA/JUSTIN LANE)

An armed British police officer stands on duty while a member of the The Life Guards sits on his horse during the Changing the Guard ceremony in London on March 22. | (ADRIAN DENNIS/AFP/Getty Images)

Russian police stand near the State Historical Museum in Moscow on March 22. | (EPA/YURI KOCHETKOV)

A Capitol Police officer watches from the U.S. Capitol building on March 22 in Washington, D.C. | (BRENDAN SMIALOWSKI/AFP/Getty Images)

A police car near the Eiffel Tower in Paris on March 22. | (LIONEL BONAVENTURE/AFP/Getty Images)

A member of the Counter Terrorism Centre patrols near Parliament in downtown Budapest, Hungary, on March 22. | (EPA/ZOLTAN BALOGH)

A pair of Metro-North Railroad Police officers patrol in New York City's Grand Central Terminal on March 22. | (AP Photo/Richard Drew)

Armed British police officers stand on duty in front of Big Ben in London on March 22. | (ADRIAN DENNIS/AFP/Getty Images)

Spanish police officers stand guard in front of the Puerta de Alcala gate in Madrid on March 22. | (EPA/PACO CAMPOS)