The European Union says it will not change Europe's passport-free system of travel despite pressure to do so amid a thwarted rail attack on a multinational rail line and a large influx of migrants into the EU.

The so-called Schengen agreement allows travel without internal border checks between 22 EU member countries plus Iceland, Liechtenstein, Norway and Switzerland.

EU Commission spokesman Christian Wigand said Monday that "Schengen is non-negotiable and the Commission has no intention of changing it."

But he said that Schengen rules allow for security to be stepped up by national police as long as actions are targeted and do not substitute for border checks.

Belgium's prime minister has said the rulebook might have to be re-examined if police are not able to provide sufficient security for travelers.