Critics blasted the EU’s free movement laws on Tuesday in the wake of the bombings in Brussels — saying they allow terrorists to strike at the heart of Europe with ease.

“This horrific act of terrorism shows that Schengen free movement and lax border controls are a threat to our security,” said Mike Hookem, defense spokesman for the UK Independence Party, which has campaigned for a British exit — or “Brexit” — from the European Union.

“The head of Europol said in February that 5,000 jihadists are at large in the EU, having slipped in from Syria. There are 94 returned jihadists currently living in Molenbeek, Brussels. This fact alone should alert people to the fact that open borders are putting the lives of European citizens at risk,” he explained.

Since 1995, the Schengen Agreement has enabled free, passport-less movement between countries within the EU. There are currently 26 nations that operate under these laws, including Belgium, France, Germany, Luxembourg, the Netherlands, Portugal and Spain.

After the attacks in Brussels unfolded, authorities across the world beefed up security at airports, train stations and other key sites.

The entire border between Belgium and France was placed on lockdown, and the Thalys train service — which runs between France, Belgium and the Netherlands — was temporarily halted as well.

Eurostar, a high-speed rail service connecting London with Brussels and Paris, also announced that trains had stopped running to and from the Belgian capital, as did Germany’s state rail system, Deutsche Bahn.

More than 200 flights to Brussels were diverted or canceled after the attacks, and security was ramped up at French and British airports, including Gatwick and London Heathrow, Europe’s busiest transportation hub.

In Moscow, officials vowed to “re-evaluate security” at Russian airports, which have been targeted by terrorists in the past, most recently in 2011.

Extra safety measures, including heavily armed police and bomb-sniffing dogs, were also put in place at airports and crowded areas in Egypt, Austria, Greece and the Netherlands.

In addition, authorities stepped up security in the Big Apple, despite there being no known threats.

Port Authority police placed anti-terrorist patrols at JFK, LaGuardia and Newark airports, as well as local bridges, tunnels and bus terminals shortly after the bombings.

Meanwhile, airline stocks in Europe dropped drastically amid fears that people would stop booking flights.

Tuesday’s terror attack comes just four months after ISIS jihadists unleashed a series of coordinated strikes in Paris, leaving 130 people dead.

While there is still no intelligence to confirm whether the bombings were carried out by Belgian citizens or people coming from abroad, many were quick to call for restrictions on free movement Tuesday — saying it ultimately helps terrorists stay under the radar.

“Brussels, de facto capital of the EU, is also the jihadist capital of Europe. And the Remainers dare to say we’re safer in the EU,” tweeted Telegraph columnist Allison Pearson.

British author Tony Parsons wrote, “Thoughts are with the people of Brussels … No nation in the world can protect its citizens without protecting its borders.”

UKIP leader Nigel Farage added, “I’m very upset by events in Brussels today and even more depressed for the future.”

With Post wires