BRUSSELS (Reuters) - EU member states reported a record 1.82 million illegal border crossings last year, a surge that made Europe more vulnerable to militant attacks, border agency Frontex said on Tuesday.

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The figure was six times more than the previous record in 2014.

Syrian nationals accounted for the largest proportion of arrivals, although the share of Afghans rose significantly towards the end of the year and Iraqis were the third largest nationality using this route.

Many of the illegal crossings were by people who were counted for the first time when they arrived on the Greek islands from Turkey and again when they crossed one of the EU’s external borders in the Western Balkans. In all, more than one million people migrated into Europe in 2015.

The Eastern Mediterranean route, especially the Greek islands in the Aegean, accounted for the largest number of detections – nearly 885,400. Apart from the rise in migratory pressure, Frontex said the data underlined Europe faced an increased militant threat.

Two of those involved in the Nov. 13 Paris attacks had entered through the Greek island of Leros and had been registered by the Greek authorities after presenting fraudulent Syrian documents, it said.

“The Paris attacks in November 2015 clearly demonstrated that irregular migratory flows could be used by terrorists to enter the EU,” Frontex said in its report.

“With no thorough check or penalties in place for those making such false declarations, there is a risk that some persons representing a security threat to the EU may be taking advantage of this situation.”

It also pointed to the routes used for smuggling weapons, often traded from former conflict regions such as the Western Balkans, where about 800,000 weapons are estimated to be in illegal civilian possession in Bosnia and Herzegovina alone.

A few days before the Paris attack, German police officers discovered pistols, hand grenades, Kalashnikov rifles with ammunition and an explosive agent. The weapons were transported from Montenegro to France in a car of a man probably linked to suspects behind the Paris attacks, Frontex said.

Although the number of illegal border-crossings detected is likely to be an under-estimation, Frontex said the upsurge in detection has also led to a surge in violent incidents along the EU’s external borders.

People smugglers have threatened border guards and the numbers of people crossing borders en masse have led to violent clashes.

The number of migrants arriving via the Central Mediterranean route fell last year by about a tenth to 154,000, largely because Syrians had switched to using the Eastern Mediterranean route, Frontex said.