EU starts border checks on everyone

"We still have a stock of 2,500 Europeans who are on the ground [Syria and Iraq] and we don't know how many, at what rhythm, and on which routes they will return here," the EU's counter terror coordinator, Gilles de Kerchove, told Belgian radio last month.

Anyone who flies in, or crosses a land or sea border will have their identities cross-checked with the Schengen Information System (SIS), and Interpol's database of lost travel documents (SLTD).

The checks, which were already being imposed on non-EU nationals, will now also extend to EU citizens.

Authorities will be able to relax some of the border control checks in case of heavy traffic flows. A transitional period has also been imposed for airports.

SIS is the most widely-used information system for law enforcement in Europe and is undergoing reforms.

A new alert category for "unknown wanted persons" will be included. Alerts will also be issued on terrorist offences and on anyone that has an entry ban.

Plans are also underway to include an automated fingerprint identification service that would allow border guards to one day search SIS using fingerprints.

Julian King, the EU commissioner for security, told MEPs in March that the fingerprint system is needed to catch people who use fake IDs.

SIS has been touted as the biggest and most successful EU-wide security database, with hits increasing from around 150,000 in 2015 to more than 200,000 last year.

Authorities had queried the database almost 4 billion times in 2016, a 40 percent increase from 2015.