A German minister yesterday warned against drawing a hasty link between refugees and perpetrators of the deadly Paris attacks, warning that the IS group could be trying to exploit the debate over Europe's migrant influx.

The French police's discovery of a purported Syrian passport near the body of one attacker in particular has sparked concerns that at least one of the assailants might have entered Europe with the hundreds of thousands of people fleeing Syria's civil war.

But Germany's Justice Minister Heiko Maas called for "very, very great prudence, until things are clear".

"We are aware that the IS [Islamic State] is known to leave such false tracks behind to politicise and radicalise the issue over refugees in Europe," Maas told public broadcaster ARD.

The questions over Europe's migrant influx are particularly sensitive in Germany, which has become the top destination for those fleeing war and persecution.

Europe's biggest economy expects to see around one million asylum seekers this year alone.

Bavarian Finance Minister Markus Soeder had cranked up pressure on German Chancellor Angela Merkel's to reverse her "open-door" refugee policy, saying the attacks in Paris underlined the need for tougher measures to control the influx of migrants.

"The days of uncontrolled immigration and illegal entry can't continue just like that. Paris changes everything," Soeder told Welt am Sonntag newspaper.

"The CSU stands behind the chancellor, but it would be good if Angela Merkel acknowledged that the opening of the border for an unlimited period of time was a mistake," Soeder said.

His comments triggered a sharp rebuke by Bavarian state premier Horst Seehofer, leader of Merkel's sister party, the Christian Social Union (CSU).

He said it was "totally inappropriate" to criticise the chancellor in times when all democrats should stand united. Seehofer added migration and terrorism were two topics that had to be separated clearly.

This echoed earlier comments from Interior Minister Thomas de Maiziere and Economy Minister Sigmar Gabriel, who both warned against making any hasty links between the assault in Paris and the refugee debate.

German officials indicated that Merkel saw no reason to revise her stance on refugees in the wake of the Paris attacks.

The head of Germany's domestic intelligence services called for "orderly procedures" regarding the handling of the daily entry of thousands of refugees and warned extremists could exploit the sometimes chaotic migration situation.

While German police are currently conducting passport checks at border crossings and in border areas, thousands of refugees are thought to be coming into the country without any checks.

TOO EARLY TO CONCLUDE

Greek and Serbian authorities have confirmed the passport belonged to a man who registered as a refugee in October on the island of Leros and applied for asylum in Serbia a few days later.

Yet on Sunday, European Commission President Jean-Claude Juncker firmly defended the EU's hotly-contested plan to redistribute refugees across Europe despite calls by Poland to scrap the scheme after the deadly attacks in Paris.

"I would like to invite those in Europe who are trying to change the migration agenda we have adopted... to be serious about this and not to give in to these basic reactions. I don't like it," Juncker told reporters on the sidelines of the G20 leaders' meeting in Antalya, Turkey.

More than 800,000 migrants have arrived in Europe by sea so far this year, mostly from the Middle East, with Germany alone expecting nearly a million migrants in 2015.

Titled "Why Syrian refugee passport found at Paris attack scene must be treated with caution", an article in The Guardian newspaper read that there are several reasons why it's worth waiting until all the facts are known before making too strong a link between the attacks and the refugee crisis.

The first is a general one: on at least 12 occasions, Isis has actually criticised refugees for fleeing to Europe. "For those who want to blame the attacks on Paris on refugees, you might want to get your facts straight," wrote Aaron Zelin, an analyst of jihad, in an online commentary about the 12 outbursts.

"The reality is, [Isis] loathes that individuals are fleeing Syria for Europe. It undermines [Isis's] message that its self-styled caliphate is a refuge." It's therefore unlikely that the vast majority of Syrians fleeing to Europe are Isis supporters, since their actions are in obvious contravention of the group's creed.

Friday's attacks in Paris that left at least 129 dead and hundreds injured also have raised fears of a similar assault by Islamist extremists on US soil.

Obama announced in September that the United States would take in 10,000 Syrian refugees by September 2016.

Various Republican presidential hopefuls insisted on Sunday that in the wake of the Paris attacks America must not take in Syrian refugees because they might include Islamic State militants.

But a White House aide said the plan to bring Syrian refugees into the country carries very little risk, because the vetting process is "robust" and the overall number of refugees relatively small.

"We cannot close our doors to these people," Ben Rhodes, Obama's deputy national security adviser told the Fox News Sunday program.

Governors of Two US states -- Alabama and Michigan --- say they will block or suspend a program to resettle Syrian refugees within their borders, citing security concerns after Friday's wave of deadly assaults in Paris.

A FAIRY TALE

The Netherlands' Foreign Affairs Minister Bert Koenders noted that "closing the borders creates the illusion that we are safe. It's a fairy tale that does not help anyone."

"We must not be naive. We have to check migrants so that we know who we are dealing with, but we need to be very careful when linking causes and effects," he added.

"I understand this fear, and we cannot completely rule out" the presence of jihadists among the migrants, but "we are dealing with terrorism that took place both before and after the wave of migration," Koenders said.

In Croatia, which has become the main Balkan country of transit for migrants, Prime Minister Zoran Milanovic reminded that "closing (borders) and barbed wire does not prevent these kind of tragedies."

Canada's new Prime Minister Justin Trudeau said that the country will still take in 25,000 Syrian refugees before January 1 but he is facing increasing pressure to tighten screening procedures and slow down the process to make sure that Islamic State infiltrators aren't among them.

Trudeau, who last month won an election fought partly on security and the refugee issue, on Sunday said "Canada is pleased to be stepping up" to take in the refugees and will integrate them into the country, reports Reuters. 

"We will be accepting 25,000 Syrian refugees between now and January 1st," Trudeau said in the written text of a speech at the G20 major powers summit in Turkey.