Updated

European Union nations pledged Friday to step up cooperation in an effort to keep the more than 600 EU citizens now fighting in Syria from veering toward terrorism upon their return home.

EU home affairs ministers said they plan to increase surveillance of social media, intensify cooperation with nations that border Syria like Turkey and urge the European Parliament to approve legislation to make suspicious travel to the region more traceable.

French Interior Minister Manuel Valls says the number of EU citizens fighting abroad with potential links to terror groups "has never been seen at this scale." He said it by far outstripped recent wars and conflicts in Afghanistan, Somalia and the Sahel region.

Valls said a survey of the eight nations most concerned about citizens fighting with the opposition in Syria showed that some 500 had left for Syria, and said the total for the EU's 27 member nations would be higher than 600.

He refused to divulge specific numbers for other nations but said some 120 Frenchmen had already gone to Syria.

"In less than two years, the mass in Syria is bigger than that what we have known" in other recent conflicts combined, he said.

Even though the EU nations, like many of the fighters, oppose the Syrian regime of President Bashar Assad, there are fears many have joined extremist groups, sometimes with links to al-Qaida.

Once fully trained, radicalized or traumatized in the Syria conflict, these fighters could form an acute danger for their home nations upon their return. Valls' fears are shared by many countries, such as Britain, Germany, Spain, the Netherlands, Belgium and the Nordic nations.

"We will proceed with a package of measures," said Irish Interior Minister Alan Shatter.

When it comes to social media like YouTube, Facebook and Twitter, the nations want the Europol police agency to investigate radical sites that propagate violence and terror. They also want to cooperate with the United States in approaching the major Internet providers to see how they can take suspicious sites off the web and eliminate dangerous content.

Terror fears have increased recently after a British soldier was slain on a London street in broad daylight and a French soldier was stabbed while patrolling a crowded area just outside Paris, even though neither was linked to returning Syria fighters.

Anti-terror measures are still largely the domain of the individual EU nations but the ministers hope the EU can pool some resources to make them more effective.