European capitals went into high security alert after Paris was rocked by terrorist attacks that threaten to open up a new dilemma for Angela Merkel and other leaders advocating an open-door policy for refugees from war zones in the Middle East.

With the French capital in shock, President Francois Hollande blamed Islamic State for the killing of at least 127 people in the city on Friday night in what could be further evidence of a shift in tactics by the Islamist terror group from the battlefields of Syria and Iraq to civilian targets in Europe.

If borne out, that pivot to Europe may give fuel to critics of the German chancellor who argue that allowing free entry to refugees risks making it easier for extremists to slip through the security net. French police said a Syrian passport was found on the body of one suicide bomber in Paris, The Associated Press reported.

“Some populists will try to abuse this and say, 'This is what you get when you let people from this region in,”' Jan Techau, director of Carnegie Europe in Brussels, said by phone. In Germany, “the security situation in the Middle East will become a much bigger issue,” he said.

For Merkel, the terror struck just as she struggles to rally the German public and her own party behind her refusal to restrict this year's record influx of refugees and migrants. In her first public comments on the attacks, she gave no sign of backing down and suggested that giving in to intolerance would hand the terrorists a victory.

“We believe in the rights of every individual to seek his fortune, in respect for others and in tolerance,” she said Saturday in Berlin. “Let us reply to the terrorists by resolutely living our values and by redoubling those values across all of Europe -- now more than ever.”