NEW YORK: Barack Obama is battling a backlash in America against his plans to accept thousands of Syrian refugees in the wake of the Paris suicide attacks by Isil terrorists.
Republican presidential candidate Jeb Bush said the US should accept only Christian refugees after it emerged that at least one attacker was a Syrian
Nine US states have said they would not accept Syrian refugees, to avoid putting American lives at risk.
In Congress, Republicans threatened to block the plans by frustrating legislation to fund the programme.
However, Mr Obama attacked critics, saying that "slamming the door in the faces" of refugees from Syria was a "betrayal" of American values.
He praised Angela Merkel, the German chancellor, for taking a "very brave stance in saying it is our moral obligation" by accepting hundreds of thousands of vulnerable refugees.
Mr Obama said: "We have to work harder. The United States has to step up and do its part. And when I hear folks say, 'well, maybe we should just admit the Christians and not the Muslims', when I hear political leaders suggesting there would be a religious test for which person... is admitted.
"When some of those folks themselves come from families who benefited from [being] protected when they were fleeing war and persecution, that is shameful.
"That is not American, that is not who we are. We don't have religious tests to our compassion."
The US president announced in September that 10,000 Syrian refugees will be allowed to enter the country next year.
However in the wake of the Paris attacks, Mr Bush suggested that any American assistance to refugees fleeing the Middle East should be primarily focused on Christians. He said: "I think we need to do thorough screening and take in a limited number."
Ted Cruz, a US senator from Texas, also said that the US should provide a "safe haven" for Christian refugees.
In Congress, Tom Price, the chairman of the House of Representatives' budget committee, said the US "must suspend our refugee programme until certainty is brought to the vetting process".
The governors of several other states, including Michigan, Texas and Alabama, also urged caution.
Rick Snyder, the governor of Michigan, said: "Michigan is a welcoming state and we are proud of our rich history of immigration. But our first priority is protecting the safety of our residents."
Mr Snyder, who a fortnight ago described himself as "the most pro-immigration governor in the country", said that he was acting in the best interests of his residents.
Robert Bentley, the governor of Alabama, said: "I will oppose any attempt to relocate Syrian refugees to Alabama through the US Refugee Admissions Programme.
"As your governor, I will not stand complicit to a policy that places the citizens of Alabama in harm's way."
Texas also announced it would not accept Syrian refugees. Referring to the Paris attacks, Greg Abbott, the governor, said: "American humanitarian compassion could be exploited to expose Americans to similar deadly danger."
But speaking at the G20 meeting of leading nations, Mr Obama said this approach was "shameful", saying: "That's not American. That's not who we are." He added: "Even as we accept more refugees including Syrians we do have to subject them to rigorous screening and security checks.
"We also have to remember that many of these refugees are the victims of terrorism themselves - that is what they are fleeing from."
Rather than casting about for a new strategy, Mr Obama said the US would intensify its current campaign of air strikes and arming and training moderate forces.
Mr Obama brushed aside those who call for sending US ground troops into the region, saying that he could send in thousands of troops to clear Isil from parts of Syria.
This "would be a mistake", he said, unless the US was committed to being a permanent occupying force in Syria.
He said: "This is not an abstraction. When we send troops in, those troops get injured. They get killed. They are away from their families."