WASHINGTON (AFP) - President Barack Obama on Wednesday slammed US "hysteria" about the security threat posed by Syrian refugees as Republicans sought to freeze a programme to resettle them in the wake of the Paris attacks.
Seizing upon fears one of the attackers may have entered Europe posing as a Syrian migrant, Republican leaders - including more than half of state governors - are trying to block a White House plan to welcome 10,000 refugees from the conflict in the coming year.
House Speaker Paul Ryan has called for a "pause" in the scheme, and lawmakers could vote as early as Thursday on a Bill that would toughen the already-lengthy vetting process for refugees from Iraq and Syria to ensure would-be attackers do not slip into the country.
In an unusually fierce rebuke on Wednesday, Obama struck out at Republicans, accusing them of demonising "widows and orphans".
"We are not well served when in response to a terrorist attack we descend into fear and panic," Obama said.
"We don't make good decisions if it's based on hysteria or an exaggeration of risks," he added, speaking from Manila.
"They are scared of widows and orphans coming into the United States of America."
Congress is under extraordinary pressure to act, after at least 27 US state governors voiced opposition to taking in further Syrian refugees, some ordering departments to halt cooperation with federal refugee programmes until tighter controls are brought in.
Some Democrats shared similar views, including senior Senator Chuck Schumer who acknowledged it might be "necessary" to pause and review the programme.
Homeland Security Committee chairman Michael McCaul said the Bill introduced late on Tuesday would make comprehensive background checks compulsory for every refugee from Syria and Iraq.
McCaul's office said the Bill would "put in place the most robust national-security vetting process in history for any refugee population."
It would require the director of the FBI, the Secretary of Homeland Security and the director of National Intelligence to certify that each refugee is not a security threat, the Republican McCaul said.
Senator John McCain, a Republican known for his often independent stances on foreign policy issues, said he supported a pause but offered a word of caution.
"I believe the overwhelming focus on the refugee program in recent days is misplaced," he said.
"I especially encourage my fellow Republicans to recognize that refugees are not the problem - they are the symptom of the problem."
The White House has held a 90-minute call with a bipartisan group of 34 governors, urging them to avoid measures that would block Middle Eastern refugees from entering the country.
Should the House legislation pass it could be a major roadblock for Obama's resettlement program.
Another Bill, by presidential hopeful Senator Ted Cruz, reportedly would ban all Syrian Muslims from resettling in the United States.
After his chamber held a moment of silence for the Paris victims, Senate Majority Leader Mitch McConnell and others also said they favored a "moratorium" on Syrian refugees.
Obama, in his remarks, defended the refugee policy, insisting the screening in place was enough to weed out militants and keep Americans safe.
"They are subjected to the most rigorous process conceivable," Obama said of the refugees.
In a tweet, he added: "We also win this fight with our values. America can ensure our own security while welcoming refugees desperately seeking safety from ISIL."
White House spokesman Josh Earnest also pushed back against the Republicans, defending the checks carried out in refugee camps in Egypt, Jordan and Turkey.
"Typically, it takes between 18 and 24 months for people to be cleared as refugees seeking asylum into the United States," he told Fox News.
"They're subjected to background interviews, a biometric information is collected from them, their information is run through national security databases."
"Only then are they allowed into the United States," Earnest said.
The refugee issue has become a political football in the race for the White House.
Several Republican candidates including Donald Trump and Ben Carson have announced strong opposition to the programme.
Trump, in an interview to air Friday, said he would ban all Syrian refugees - Christians and Muslims - from entering the country.
"The problem is, we don't (know) if they're Christian or not," Trump said in excerpts released by ABC News.
The top Democrat in the race, former secretary of state Hillary Clinton, lashed out at suggestions from Cruz and Jeb Bush that aid be prioritised for Christian refugees over Muslims.
"The idea that we'd turn away refugees because of religion is a new low," she tweeted.
More than four million Syrians have fled their homeland since the war began.
Between Oct 1, 2011 and Nov 14 of this year, the United States admitted 2,159 Syrian refugees, according to the State Department.
That slow pace is due largely to the comprehensive screening already in place.