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By Andy Eckardt

MAINZ, Germany — Two Syrians who were registered as refugees after making their way to Austria have been detained amid claims they previously fought for ISIS.

A spokesman for the prosecutor’s office in Salzburg confirmed to NBC News today that two separate investigations were ongoing against "two Syrian men in their 20s."

The two men were reported to authorities by other migrants who were concerned by both their behavior and background stories. Authorities say they reportedly had discussed their involvement in ISIS combat.

“There is no evidence that the men planned terror attacks in Europe and there is no evidence of a connection to recent attacks," the prosecutor's office spokesman added.

Both men were being held in so-called "investigative custody" in Austria. The probe is ongoing.

Authorities have turned their attention to the issue of how to secure Europe's borders and the screening of migrants since the Paris attacks. One of the suicide bombers arrived at the Greek island of Leros on a boat from Turkey packed with 198 other people.

He later requested asylum at the Presevo border crossing in Serbia — which is also part of a route regularly used by refugees fleeing war-torn Syria as well as other migrants seeking better lives in the West.

Related: Here's Why Europe Can't Pull Up Its Drawbridge

The attacker used a Syrian passport bearing the name Ahmad Almohammad but French police last month launched an appeal for information about his real identity. He was tied to the ISIS-linked attacks through fingerprints after blowing himself up near an international soccer game.

Under the Schengen Agreement of 1995, travel without passport checks is permitted within 26 countries on the European mainland. That means once migrants arrive in a country like Greece, they are free to make their way across huge swaths of the continent without facing border controls.

However, some countries introduced checks in the wake of the Paris attacks.