The mastermind behind the Paris terrorist attacks entered Europe posing as a Syrian refugee, it has emerged. At least two of the terrorists who carried out the attack are also thought to have slipped in among the hundreds of thousands of migrants making their way across the continent, prompting a senior French security official to comment that Europe’s borders are “like a sieve”.

Abdelhamid Abaaoud, the 27 year old Belgian thought to be behind the attacks is one of more than 5,000 Europeans who have travelled to Syria and Iraq to wage holy war. But Europol has now admitted that the details of only 2,000 of those who have gone have been logged onto an EU-wide database, meaning that authorities have no way of checking the backgrounds of the remaining 3,000 or so, The Telegraph has reported.

Abaaoud and at least two of his fellow jihadists gained entry to Europe via Greece, a route taken by nearly 700,000 migrants this year, according to the UN’s refugee agency. The mass movement of people offered the perfect cover to the terrorists, who were able to use Syrian passports to gain free passage across borders.

A senior member of the DGSE, France’s equivalent of MI6, told AFP: “It has to be said: Schengen is a sieve. A guy with a CV and history like this, wherever he turned up in Schengen, he should have sparked a red flag.”

Speaking to a committee meeting of MEPs, Rob Wainwright, the director of Europol and a former intelligence officer in MI5 admitted that only a handful of countries currently contribute data to the Focal Point travellers system, designed to share the details of known jihadists in order to disrupt plots.

“We are only confident we have 2,000 names in the system, even though the general assessment across Europe is there are at least 5,000 European nationals who have travelled to Syria and Iraq,” he said.

The security services are now “urgently scrutinising” the links between migrant smuggling rings and the Paris terror cell, he said, adding “We all have seen in the media the reports of possible connections with, for example, a stolen Syrian passport.

“What this indicates, perhaps, is connection with the migration crisis, or illegal rings of people smugglers. It is too early for us to confirm this link exists, but Europol is prioritising its focus on trying to determine that at this moment.”

Europe’s home and interior ministers are expected to agree tightened security measures at the external borders of the Schengen zone, at a summit in Brussels today. Emergency plans have been drawn up to ensure that everyone travelling into the Schengen Zone will have their details checked against the Schengen System Watchlist, a database used to flag criminals.

Currently EU passport holders only undergo a cursory visual passport inspection, to respect their “freedom of movement”.

Bernard Cazeneuve, the French interior minister, said French intelligence had not even been aware that Abaaoud was in the country until after the attacks had taken place, adding that other states had provided no intelligence as to his whereabouts. He demanded Europe “pull itself together”.