Hungary's prime minister, the strongly anti-immigration, Viktor Orban, told lawmakers Monday that the EU plan to distribute migrants among member countries is unlawful and will "spread terrorism around Europe."
Orban said no one could say for certain how many terrorists entered Europe by blending in with migrants, but "one terrorist is too many."
Orban said the EU needs to "forget political correctness ... and return to common sense" by adopting policies to protect its external borders, its culture and its economic interests and ensure that people are given the right to influence EU decisions.
Hungary has built fences on its borders with Serbia and Croatia to divert the flow of migrants.
Marine Le Pen, the leader of France's far-right National Front party, has called for a tightening of the country's borders in response to the attacks. "By spreading out migrants through the villages and towns of France, there is a fear that terrorists will take advantage of these population flows to hit out at us," she said after meeting the French president on Sunday.
Europe is already sharply divided over how to handle the arrival of hundreds of thousands of refugees from wars in Syria, Iraq, Libya and elsewhere, and the possibility that one of the attackers may have entered Europe among the thousands of asylum-seekers could have far-reaching political consequences on the continent and elsewhere.
Bavarian allies of German Chancellor Angela Merkel called for a reversal of her "open-door" refugee policy, saying the Paris attacks underlined the need for tougher controls.
"The days of uncontrolled immigration and illegal entry can't continue just like that. Paris changes everything," Bavarian finance minister Markus Soeder told the Welt am Sonntag newspaper.
Meanwhile, a G-20 summit in Turkey took on more urgency. Turkish President Recep Tayyip Erdogan on Sunday urged the gathered world leaders to prioritize the fight against ISIL, saying the Paris attacks showed the time for words is over.
Hollande pulled out of the summit to stay in Paris. On Saturday he vowed that France would be “merciless” in its efforts against “these barbarians from Daesh,” using an Arabic acronym for ISIL.
On Monday, Defense Secretary Ash Carter made during his first public appearance since the Paris attacks, saying "We're looking for opportunities to get at them, and we'll continue to do that until they're defeated."
Those methods include strikes on oil infrastructure and identifying and aiding ground forces, Carter said.
President Barack Obama on Sunday pledged solidarity with France and said the U.S. would “redouble” its fight against ISIL.
The armed group on Sunday evening released a video in which one of its fighters in Iraq vowed to attack Washington in the same manner as Paris.
The fighter warned nations that are taking part in the "Crusaders' campaign" against the group, saying that as "we struck France on its ground in Paris we will strike America on its ground in Washington."
Al Jazeera and wire services