BRUSSELS (AFP/REUTERS) - Security at cities around the world has been boosted in response to the deadly attacks in Paris, France on Friday (Nov 13).

The Belgian authorities said on Saturday (Nov 14) they have boosted checks on their borders, especially with France, following the attacks in Paris that have left at least 120 people dead.

"Reinforced border checks have been established on the borders within the framework especially of a close collaboration with the French authorities," according to Belgium's national centre for threat evaluation, OCAM.

A spokesman for Prime Minister Charles Michel said the premier would convene his security cabinet at 9am on Saturday, the spokesman added, to review responses to the violence affecting Belgium's southern neighbour.

Coming after several months in which movements of migrants from the Middle East, Africa and Asia have prompted some EU states to suspend elements of the bloc's open-border system, the spokesman stressed Belgium was not closing its frontiers but would step up spot checks on travellers arriving from France.

Italy is adopting heightened security measures following the attacks, Prime Minister Matteo Renzi said, adding the risk of further deadly attacks should not be underestimated. Mr Renzi was to preside over an extraordinary meeting of Italy's national security council.

Berlin police on Saturday boosted security in the German capital, with barricades put up at French sites including the embassy. "We have adjusted our protection measures overnight," a police spokesman told AFP, although she would not give details.

The French embassy next to the Brandenburg Gate was blocked off, and flags were flying at half mast. Dozens of people had also gathered in front of the embassy where they left flowers and candles as a sign of solidarity.

The New York Police Department said it had bolstered security at high-profile locations around the largest US city on Friday in response to what officials believe were coordinated attacks in Paris which have killed at least 140 people.

After news of the carnage, officers from the NYPD's Counterterrorism Response Command and other special units were deployed to guard areas of the city that attract tourists, as well as the French Consulate in midtown Manhattan, police said.

"Teams have been dispatched to crowded areas around the city out of an abundance of caution to provide police presence and public reassurance as we follow the developing situation overseas," the NYPD said in a statement.

New York City, the site of the 2001 strike on the World Trade Center that killed nearly 3,000 people, is considered a top target for attacks by Islamist extremists. "Specific deployments, at French government locations in New York City, were made immediately after the attacks," the department said.

The spire at One World Trade Center was lit up on Friday night with blue, white and red, the colors of the French flag.

Even though there was no known imminent threats, "until we know more, we are deploying more police", the department said.

Police did not say how many extra officers were sent to guard the areas of concern nor did they specify the areas where the extra officers were sent.

New York Mayor Bill de Blasio said on Friday the city was on constant alert and ready for any potential attacks that may follow the mayhem in the French capital. "Every time we see an attack like this it is a reminder to be prepared to be vigilant," Mr de Blasio told ABC 7 television.

New York Governor Andrew Cuomo said he directed state law enforcement officials to monitor the Paris "situation for any implications in New York state and remain in constant communication with their local and federal partners".

The Port Authority of New York and New Jersey said police were on heightened alert at all of the agency's bridges, tunnels and rail facilities, as well as at the World Trade Center in lower Manhattan.

It said it was increasing patrols and checking of bags, buses and trains.

US Department of Homeland Security Secretary Jeh Johnson said in a statement that "we know of no specific or credible threats of an attack on the US homeland of the type that occurred in Paris tonight".

Mr Johnson said in a statement that the FBI and DHS are closely monitoring the situation, and the agencies are in contact with their counterparts in the region. He added the DHS and the FBI, out of an abundance of caution, are consulting with state and local law enforcement in the United States.

The National Basketball Association, which had 11 games on the schedule Friday night, said it was increasing security at each of the venues. The most popular sport, American football, would not have any games until Sunday as previously scheduled.

"Security at our games is always at a heightened state of alert," National Football League spokesman Brian McCarthy said.

Outside of New York, law enforcement and transportation agencies said they were also on high alert.

The US Capitol Police in Washington boosted patrols around the Capitol complex, a spokesman said. "There is currently no known threat to the Capitol Complex," she said in an e-mail.

The Metropolitan Police Department in Washington has "out of an abundance of caution" deployed additional law enforcement resources to French-owned sites and other high-profile locations, said Officer Sean Hickman. Mr Hickman said there was no imminent threat to the district.

In Boston, the police department said it deployed additional resources and was working closely with federal authorities, but saw no credible threat in the city, where Islamist militant sympathizers set off homemade bombs at the Boston Marathon finish line in April 2013.

Massachusetts State Police said they took "several actions" after the Paris attacks, including increasing security around the State House in Boston. "A multi-layered security package is in place at Logan International Airport," the police said in a statement.

The St Louis Police Department said it added an extra layer of security for the World Cup soccer qualifying match between the United States and St Vincent Friday evening.

Chicago police said they were following developments in France to determine whether to bolster city security but that there were no immediate threats.

"Tonight the City of Chicago stands shoulder to shoulder with the City of Paris in the wake of today's despicable and horrifying attacks," Mayor Rahm Emanuel said.

In Pittsburgh, which was hosting a National Hockey League game on Friday, a police spokesman said public safety personnel were working with intelligence authorities to identify any indications of local threats.

Amtrak, the US passenger train service, said it was monitoring the events in Paris but said there were no specific or credible threats against it.

American Airlines Group , the world's biggest carrier by passenger traffic, said on Friday it was delaying flights to Paris in response to the explosions and shooting attacks there, even though French airports remained open.

"Currently Charles de Gaulle International Airport is open, however, we are holding our remaining departures this evening to Paris until we have additional information," American Airlines spokesman Joshua Freed said.

United Continental Holdings said its three scheduled flights would still depart for Paris on Friday evening from hubs in Chicago, Newark and Washington, D.C. "We're operating our schedule as planned," spokesman Charles Hobart said.

A Delta Air Lines Inc spokesman said that currently, its flights were operating normally between the United States and Charles de Gaulle. He said Delta was in touch with its partners, Air France KLM Royal Dutch Airlines, and was "not aware of any changes to their operations".

A spokesman for the Federal Aviation Administration said the agency was "following the situation closely and remains in close contact with our security and law enforcement partners".

"The agency is prepared to act quickly in the event action is warranted," she said.

The French Foreign Ministry said airports would remain open, and flights and train service would continue.

"Airports continue to function. Airline flights and train services will be assured," the ministry said in a statement.

Finland also stepped up border checks in Helsinki airport and at ports, and police were on heightened alert following Friday's attacks in Paris, the government said, while neighbouring Russia announced that they would implement transport safety measures across Russia.