Major cities in the U.S. have bolstered security after a series of terror attacks in Paris Friday left at least 127 dead.
The New York Police Department dispatched its "critical response group," which is equipped with high-powered weapons, and other security to crowded areas of the city on Friday.
Additional officers were deployed to the French embassy and French government sites in the city, NBC New York reported. Police said there was no known credible threat, but the extra security measures were being taken "out of an abundance of caution."
"At this time, we know of no specific or credible threats of an attack on the U.S. homeland of the type that occurred in Paris tonight," Secretary of Homeland Security Jeh Johnson said Friday.
French president Francois Holland on Saturday blamed ISIS for the attacks, describing the violence as an "act of war."
President Barack Obama called the violence an assault not just on France, but "an attack on all of humanity."
"Once again, we've seen an outrageous attempt to terrorize innocent civilians," he said.
New York City's Empire State Building and World Trade Center were lit in blue, white and red in solidarity with the French people.
U.S. Capitol Police said it was monitoring developments and there may be extra patrols. Chicago police said the department was working in coordination with federal officials.
The Southeast Florida Fusion Center, which focuses on the Miami area, was monitoring events and the Miami-Dade Police Department has asked their patrol officers to be on alert.
Police in Los Angeles were stepping up patrols at a half dozen events, including separate Justin Bieber and Snoop Dogg concerts over the weekend, officials said. San Francisco police were also on "high alert," officials said.
The Boston Regional Intelligence Center was "on it from the beginning" according to a senior law enforcement source.
Boston Police stepped up patrols around French sites and were assisting police in Cambridge to monitor sensitive sites there, a senior official said.
The Massachusetts State Police said they were increasing security around key government sites and they have a "multi-layered security package" in place at Boston's Logan airport.
The NBA said security would be increased at games, and the NFL said security at its games was always at a heightened level of alert.