“Our data systems must be complementary, searchable, interoperable, and interconnected with one single click,” EU commissioner for home affairs Dimitris Avramopoulos told reporters in Luxembourg, where EU interior ministers are meeting.

He said the system would be developed “within the framework of gradually developing a single searchable interface to facilitate the job of law enforcement authorities”.

The single interface is still at the concept stage, but it is likely to be discussed at length at the next ministers' meeting in June.

Dutch interior minister Ard van der Steur said it was likely to pose legal and practical problems.

However, he was unable to cite examples when asked, saying only that such problems would be encountered “along the way”.

'Foreign fighters'

The announcement comes as the angry backlash continues against the so-called EU passenger name record (PNR), adopted on Thursday.

PNR gives police access to information like names, addresses, phone numbers, credit card details, travel itineraries, and ticket and baggage information.

Civil society groups say this could violate fundamental rights, and other critics argue that a lot of this information is already available to police through the advanced passenger information (API) database.

In addition, critics point out that most of the terrorists behind the attacks in Paris and Brussels were already known to the police.

But the authorities insist they need PNR to track EU nationals who leave and return after fighting alongside militant groups in Syria or Iraq.

The EU commission, in figures updated earlier this month, estimates there are now roughly 4,000 Europeans classed as “foreign fighters”, about 30 percent of whom are thought to have returned to Europe.

Belgium has the most foreign fighters of any member state proportional to its population.

About 200 are thought to be still in Syria with fears mounting some are returning and may plan further attacks.

"We know these people are possibly coming and certainly because pressure is higher now in Syria," said Belgian interior minister Jan Jambon.

Smart borders

An EU official insisted that the new single interface would not mean that “the cop on the street will have access to PNR”.

Instead, the plan is to bridge centralised information systems like the Schengen Information System (SIS), the refugee fingerprint database Eurodac, the Visa information system (VIS), and the EU PNR among other databases.

Plans are also under way for a new main system known as the Entry-Exit System (EES) that will track everyone who enters Europe by requiring fingerprint and facial scans.

This includes all visiting third nationals but may extend to EU citizens should the French government, which wants blanket coverage, have its way.

Law enforcement, at various levels, have access to the databases.

A supposed lack of information sharing among national security and intelligence agencies has been raised repeatedly since the Paris attacks at the offices of satirical magazine Charlie Hebdo.

Each attack prompted announcements by EU leaders to better coordinate their data but frustration at the lack of progress continues to surface after each terrorist attack.

Interior ministers, who had gathered last November in the wake of the Paris shootings and bomb attacks that killed some 130 people, made similar promises to share data. They then said it again after the Brussels bombings.

“Internal security is a national competence but terrorism is not limited to national borders,” said Avramopoulos.