A victim receives first aid by rescuers, on March 22, 2016 near Maalbeek metro station in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. EMMANUEL DUNAND/AFP/Getty Images

Airports in the Netherlands, and the European capitals of Paris and London stepped up security following explosions at the Brussels Airport and the city's metro early Tuesday. At least 23 people have been reportedly killed in the blasts, which closely follow a crackdown by local authorities on terror cells in the Belgian capital.

The country also closed its border with France following the suicide blasts and Prime Minister Charles Michel called for a meeting of his national security advisers, and warned the public to “avoid any movement” for the time being, as the terror level was raised to the maximum. Michel called for “calm and solidarity” in the wake of the blasts as it is a "black day" for the country.

French Interior Minister Bernard Cazeneuve said that an additional 1,600 police are being deployed at its borders, stating it was "essential to maintain a vigilance" in the wake of the Brussels attacks.

German federal police tightened security at the country's largest airport in Frankfurt Tuesday, while operations at the Brussels Airport have been suspended until early Wednesday. At least 13 people were reported dead in the explosions at Brussels Airport, while there were unconfirmed reports of 10 people killed in the blasts at the metro stations.

Dutch police stepped up security patrols at airports and tightened checks at borders after the attacks in neighboring Belgium, the security agency reportedly said. Security measures have also been reinforced at the Charles De Gaulle airport in Paris, an airport source told Agence France-Presse.

Belgium has "again been hit by cowardly and murderous attacks. Our hearts go out to the victims and next of kin. The Netherlands stands ready to help and support our southern neighbors in any possible way," Dutch Prime Minister Mark Rutte said, according to the Associated Press. He said "extra alertness is necessary, also in our country. We will take all necessary precautionary measures."

Rutte called a meeting Tuesday of his government's Ministerial Crisis Committee to discuss the Brussels attacks.

Authorities at London’s Heathrow Airport said they “are working with the police who are providing a high visibility presence at Heathrow.”

Meanwhile, the New York Police Department said it has ramped up security at mass transit points, bridges and tunnels, and other landmarks in the city following the attacks in Brussels.

Russian President Vladimir Putin also condemned the "barbaric" attacks in Brussels.

"President Putin has already offered his condolences to King Philippe of Belgium over death of civilians in a series of explosions in Brussels. The president strongly condemned the barbaric crimes that have been committed," Kremlin spokesman Dmitry Peskov said.

Meanwhile, Alexei Pushkov, the head of the Foreign Affairs Committee in the lower house of the Russian Parliament, reacted to the Brussels attacks by taking a shot at NATO's Secretary General Jens Stoltenberg, saying: "While Stoltenberg is fighting the imaginary “Russian threat” and putting troops in Latvia, people are being blown up under his nose in Brussels.”

British Prime Minster David Cameron said he was “shocked” and “concerned” by the explosions Tuesday, adding that he will chair an emergency response meeting in Brussels over the event later in the day.

Martin Schulz, president of the European Parliament, also condemned Tuesday's incidents as “heinous attacks.”

Donald Tusk, president of the European Council, said the Brussels attacks “mark another low by the terrorists."

I am appalled by the bombings this morning at Zavantem airport and the European district in Brussels which have cost several innocent lives and injured many others. I extend my sincerest sympathies to the relatives and friends of the victims. These attacks mark another low by the terrorists in the service of hatred and violence. The European institutions are hosted in Brussels thanks to the generosity of Belgium’s government and its people. The European Union returns this solidarity now and will fulfill its role to help Brussels,Belgium and Europe as a whole counter the terror threat which we are all facing.

Here are some more reactions to the Brussels attacks:

"Overwhelmed by heinous attacks to Brussels National and Brussels metro ds. Our thoughts to the victims, families and emergency services," Belgian Royal Palace wrote on its Twitter account.

Dutch politician Geert Wilders, wrote on his Twitter account: "We must immediately close our borders and returned Foreign rebel fighters in the Syrian Civil War preventive + lock picking . Safety comes first NL."