WASHINGTON — The Paris attacks have exposed an ideological cleavage in western countries over the handling of the Syrian refugee crisis, with the political left and right at odds over welcoming migrants.

The sharp contrast was driven by news that the group of killers appeared to include at least one accomplice who'd slipped into Europe in the human wave flowing from Syria.

That prompted a chorus of right-wing voices demanding that western governments slam the door, in what they described Monday as an unprecedented security emergency.

On the other hand, left-wingers insisted upon the moral obligation to continue screening — and bringing in — migrants affected by a humanitarian catastrophe.

The debate swiftly inserted itself into the U.S. presidential election.

The Obama administration faces a noisy political backlash — despite having promised to take in a relatively paltry number of refugees compared to its northern neighbour.

The U.S. is accepting barely a fraction of the refugees per capita that Canada's Trudeau government has promised to bring in by the new year — 10,000 for the U.S. next year, compared with 25,000 for Canada within six weeks.

But that's still too many according to Republican presidential candidates, members of Congress and more than a dozen mostly Republican state governors who demanded a halt Monday.

That uproar from the American right was echoed in France by the Front National's Marine Le Pen, by some other European parties, and by a few conservatives in Canada including Saskatchewan Premier Brad Wall.

President Barack Obama, however, pushed back against demands for a freeze. He was especially scathing of Republicans who appeared to demand a Christians-only refugee policy.

"The United States has to step up and do its part," Obama told a news conference at the G20 in Turkey.

"And when I hear folks say that, well, maybe we should just admit the Christians but not the Muslims, when I hear political leaders suggesting that there would be a religious test for which person who's fleeing from a war-torn country ... that's shameful. That's not American, it's not who we are."

An administration official was even more defiant. She told a conference in Washington that the U.S. could expand its refugee target — not shrink it.

Catherine Wiesner, deputy assistant secretary of state, told the Center for Strategic and International Studies: "The refugee resettlement numbers will hold. ... You may even see them increase."

She called the heightened politicization of the crisis a serious concern, accusing people of fear-mongering. "Some of it feels really cheap," she said, citing online rumours that 10,000 Syrians had arrived in New Orleans. The actual number? Fourteen she said — the equivalent of barely two families.

The Syrian conflict has created a historic crisis involving four million refugees, almost one-quarter of whom have attempted to reach Europe in a humanitarian emergency that has forced rivals Russia, the U.S., and Iran to speak to each other in the hope of brokering a peace plan.

It's emerging as a 2016 U.S. election issue.

Republican presidential candidate Donald Trump has warned the refugees could be, "one of the great Trojan horses"; his rival Ted Cruz wants to bar Muslim refugees, but allow Christians; Jeb Bush didn't go quite as far as Cruz, but said Christians should be a priority; Marco Rubio said the U.S. is incapable of handling the load.

A number of governors, almost all of Republican, have told Obama they don't want refugees. Some personally informed him in writing.

"I — and millions of Americans — implore you to halt your plans to accept more Syrian refugees in the United States," Texas Gov. Greg Abbott wrote in a letter to Obama.

"A Syrian 'refugee' appears to have been part of the Paris terror attack. American humanitarian compassion could be exploited to expose Americans to similar deadly danger."

Some American liberals said the furor reminded them of last year's hysteria over Ebola, fanned vigorously by Republicans right until the midterm elections ended.

In that scare, Canada's Harper government frustrated humanitarian groups and liberals abroad by imposing a visa ban on Ebola-affected countries.

This time, the political dynamic in Canada has switched.

It's now Canadian conservatives on the outs, in opposition in Ottawa and most provincial legislatures.

The Saskatchewan premier who has asked the Liberal government to suspend its refugee plans is a rare conservative in power.

Alexander Panetta, The Canadian Press