PARIS - Europe has for 30 years allowed most of its citizens to travel freely from one country to the next, but the experiment in open borders is now facing calls for its end amid several new threats.

"We face a diffuse terrorist threat trying to attack our values," French Interior Minister Bernard Cazeneuve told an emergency meeting of foreign ministers from France, Germany, Spain, Italy and other European nations, who met in Paris to deal with terrorism and improve security in the wake of the attack by gunman Ayoub El-Khazzani on the Amsterdam-Paris Thalys train last week.

At the heart of the discussion was whether or not the European Union border policy of free travel, known as "Schengen," can survive the waves of growing attacks against civilians in Europe.

The "perfect storm," as a European diplomat called it, has hit Europe: terrorism, a migration crisis, and crime. Although they are not directly connected, the perception among many seasoned Europe observers is that the free movement of people across borders is making it easier for waves of people who intend to commit acts of violence to prey on victims - and to escape prosecution.

The Schengen border-free travel area for 400 million European Union (EU) citizens (as well as non-EU nationals and other persons legally present in the EU) has some history: it was created by an agreement in 1985 by individual nations when European nations could not agree to eliminate all border controls. It grew to where, by 1999, it became part of European Union law. Today, it consists of 26 countries, although UK and Ireland opted out and other non-EU countries were included.

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According to Dimitris Avramopoulos, Commissioner for Migration, Home Affairs and Citizenship of the EU: "The free movement of persons is a fundamental right guaranteed by the EU to its citizens." As such, the Schengen area gives EU citizens the right to travel, work and live in any EU country without restrictions and "to cross internal borders without being subjected to border checks."

But concern over terrorism, illegal migration, and crime has some European countries raising alarm bells and calls for changes to the open border agreement.

The migrant crisis is adding to the security dilemma with waves of refugees moving through Europe. Several United Nations agencies are trying to cope with the crisis. U.N. Refugee agency (UNHCR) spokesperson Melissa Fleming said, at a press briefing last week at the Palais des Nations in Geneva, that the number of refugees and migrants crossing the Mediterranean this year has now exceeded 300,000, and 2,500 refugees and migrants have died or gone missing this year, trying to reach Europe.

And because there is so much confusion about refugees and migrants, UNHCR published a clarification about the 60 million people forcibly displaced, saying that refugees are persons fleeing armed conflict or persecution, and migrants are persons who chose to leave for other reasons including improving their life or family unification. UNHCR said that the large numbers of people arriving in Europe are both.

The train gunman, Ayoub El-Khazzani, was brought into French courts where the French prosecutor said he had the intent to carry out a terror attack and watched a Jihadi video before the attack, contradicting his claim that he is a common criminal who wanted to rob the train, CBS News correspondent Charlie D'Agata reported from Landstuhl, Germany.

At the Paris meeting, the French interior minister, Cazeneuve, was clear that security is vital: "In the context of terrorist threat that feeds hatred and which is constantly changing, we commit to strengthen our cooperation to ensure the safety of our citizens in order to counter any attempt to violent extremism."

But, because of the staggering numbers of both migrants and refugees, many undocumented people fleeing persecution and seeking a better life are now traveling through Europe, and without resources or jobs, some observers link them to the uptick in crime in many European cities.

Chancellor Angela Merkel of Germany has been outspoken about the migration crisis and the need to make changes to the asylum system.

New York Times correspondent, Marlise Simons, based in Paris who has covered Europe extensively, told CBS News: "Terror and crime are two very separate issues, but there is a connection, because of eastern European criminal networks that prey on the influx of people who are traveling through Europe, police say. In the villages around Paris, bands have swept in over the past few summers, stealing farming machinery, which is usually unguarded, and a number of villages near Mantes- La Jolie have dug trenches around playing fields and communal green spaces and some have put up boulders."

In May, at the United Nations Jürgen Stock, Secretary General of INTERPOL told the Security Council that in 2014, less than 900 foreign terrorist fighters had been identified through INTERPOL channels. And in 2015, more than 4,000 are available in their databases.

"We are determined to pursue our cooperation to ... prevent, detect and better fight violent acts that radicalized individuals may want to commit on European Union soil," Cazeneuve said.

At the Paris meeting, Cazeneuve read a joint statement by the European Union interior and transport ministers that outlined several methods to deal with the crisis, including spot checks as well as the call to reinstate some type of border controls, "We invite the Commission ... to examine a targeted amendment to the Schengen frontier code allowing controls where necessary and when necessary."

"We are committed to supporting, at national level, the efforts of the various security services, civil and military, private and public, in order to operate in a coordinated manner all available resources, and improving public awareness to the terrorist risk ," the statement said.

European Union Transport Commissioner Violeta Bulc said security must be proportionate to the threat and that public transit must remain open.

John Miller, deputy commissioner for the New York Police Department and former FBI deputy director told CBS News that Europe could learn from New York City's experience in dealing with the many similar threats to its transit system.

"The recent train attack reminds us that terrorists continue to focus on mass transit," Miller said. "In New York City, for a number of years we have applied tools from radiation detection, to random bag checks to roving heavy weapons teams. The deployments are intelligence-based and purposefully fluid and unpredictable. Moving to spot checks is a prudent and proportionate step."