Without yielding to terrorists' aim of inciting fear, officials around the world now provide guidance and reassurance. They say -- if only out of prudence -- people should take seriously threats by the terror group ISIS.
Here's what French, U.S., and UK officials say about what the public should do about a threatened attack and what should be done in the aftermath of one. In the meantime, a U.S.-led military coalition and French forces have intensified airstrikes on ISIS in Syria.
French President Francois Hollande set an international tone as Paris mourned the loss of 129 lives and the wounding of hundreds more in last week's attack.
"I call for unity, for people to pull together and stay calm," Hollande said in a statement.
Besides urging calm, Hollande also declared a national emergency in his country and deemed the terror attacks "an act of war." The Parliament extended that national emergency.
But his emotional appeals have served to be equally powerful.
"France is strong, and even though it may be wounded it always gets back up, and nothing will be able to hurt it, even if we are plunged in grief," the French President added. "France is robust, it is active, France is valiant and it will triumph over barbarism; history reminds us of this, and the strength we're capable of harnessing today convinces us of it."
U.S.: Turn fear into 'healthy awareness'
In a joint televised address on Thursday, U.S. Attorney General Loretta Lynch said U.S. authorities take all threats seriously and are actively defusing potential terror activity, but FBI Director James Comey added his agency isn't aware of "any credible threat here of a Paris-type attack."
"And we have seen no connection at all between the Paris attackers and the United States," Comey said.
Lynch echoed the French President in highlighting the most important things a citizen ought to do.
"We need to say we will not let our actions be overtaken by fear," Lynch said. "We will not allow merchants of violence to rob us of our most precious ideals.
"They want us to live in fear, and we refuse," Lynch said. "They want us to change who we are and what makes us quintessentially American, and that we will never do."
Many fears arise from nothing more than ISIS propaganda, Comey said.
Speaking practically, Comey urged Americans to turn any of their fears "into healthy awareness of what's around you."
Citizens should report to authorities any suspicious activity -- such as if "you heard something that didn't seem right or you read something online that seemed off," Comey said.
"If you see something that gives you a bad feeling, tell somebody in law enforcement," Comey said.
"If it's nothing, no harm done," Comey added. "But if it was something, great harm may be avoided. But counterterrorism is what you pay us to do. Tell us what you saw and then go on living your life while we do our work."
"That is channeling fear into something healthy, which is awareness of your surroundings, and not something disabling," Comey said. "That's what we hope you will do."
In New York, police are deploying additional members of its new anti-terrorism squad out of extra vigilance after a new ISIS video threatening an impending attack there.
New York Mayor Bill de Blasio encouraged the nation's most populous city to go about its normal business.
"The people of New York City will not be intimidated," the mayor said. "We understand it is the goal of terrorists to intimidate and disrupt our democratic society. We will not submit to their wishes."
While Police Commissioner Bill Bratton said New York has long been a terror target and the video offers nothing new, he condemned the objective of terror.
"We cannot be intimidated and that's what terrorists seek to do. They seek to create fear. They seek to intimidate. We will not be intimidated and we will not live in fear," Bratton said.
United Kingdom: An online guidebook
After the Paris attacks, UK counterterrorism officials reminded people in their own country that a terror attack there remains "highly likely," as it has been since August 2014, and issued a new round of advice to citizens, even renewing online a guidebook on how to recognize a terrorist threat.
As police may increase their ranks in some areas, "Don't become fearful or withdraw from the streets," the UK National Counter Terrorism Security Office said.
UK officials also urged the public to report suspicious behavior as a way to disrupt attack planning.
In the event of a weapons or firearm attack, UK authorities offered specific advice:
- Escape if you can
- Consider the safest options
- Is there a safe route? RUN. If not, HIDE
- Can you get there without exposing yourself to greater danger?
- Insist others leave with you
- Leave belongings behind
- If you can't RUN, HIDE
- If you can see the attacker, they may be able to see you
- Find cover from gunfire such as substantial brickwork or heavy reinforced walls
- Be aware of your exits
- Try not to get trapped
- Be quiet, silence your phone
- Lock and barricade yourself in
- Move away from the door
- Call police: What do the police need to know?
- Location: Where are the suspects?
- Direction: Where did you last see the suspects?
- Descriptions: Describe the attacker, numbers, features, clothing, weapons
- Provide further information: Casualties, type of injury, building information, entrances, exits, hostages
- And stop other people entering the building if it is safe to do so
When police arrive, they may point guns at you, treat you firmly, question you, and be unable to distinguish you from the attacker.
You ought to remain calm, keep your hands in view, avoid sudden movements that may appear a threat, and follow officers' instructions, the UK guidance says.