WASHINGTON: As Europe grapples with a flood of refugees from the Syrian war and the pope urges Catholics to help them, the US government may lack the political appetite to offer American soil as a safe haven to more than the current trickle of Syrians.

Refugee and immigrant groups had urged the United States to admit more Syrian refugees long before the crisis erupted this summer in Europe.

Some hoped global outrage over images of a drowned Syrian toddler in Turkey last week, and Pope Francis' call on Sunday for European parishes to take in refugees - coming just two weeks before a trip to the United States - might help prod the United States into action.

"The US could and should be doing more. The silence of the White House on this is unacceptable," said Michelle Brané of the Women's Refugee Commission.

A White House spokesman said on Monday the Obama administration "is actively considering a range of approaches to be more responsive to the global refugee crisis, including with regard to refugee resettlement."

Spokesman Peter Boogaard said in an emailed statement that the US had provided over $4 billion in humanitarian assistance since the Syrian crisis began and more than $1 billion in assistance this year." He added: "The US is the single largest donor to the Syrian crisis."

But moral arguments about the refugees' plight may be overshadowed by the political realities in Washington.

Some congressional Republicans have said allowing in Syrian refugees would constitute a pipeline for terrorists.

"The rhetoric has been really awful," said James Zogby, president of the Arab American Institute. "The difficulty of doing it is met by this Islamophobia and conflation of Syrians and Iraqis with terrorists.

"Hopefully, the pope will be able to challenge that mindset and soften some hardened hearts, but that remains to be seen."

The administration itself is concerned that militants from Islamic State or al Qaeda might slip into the country as refugees. The State Department has cited Washington's vetting process as a crucial but complicating factor for Syrians seeking entry.

Since the start of the Syrian war in 2011, Washington has accepted 1,500 Syrian refugees, most of them this year, and the State Department expects 300 more by October.

The number is tiny against the backdrop of the European refugee crisis in which Germany is preparing for 800,000 asylum seekers this year, around 1 percent of its population, and compared with the overall number of 4 million Syrian refugees.

British Prime Minister David Cameron pledged on Monday to take in up to 20,000 refugees from camps in Syria over the next five years, responding to public pressure to help.

While President Barack Obama, a Democrat, does not need congressional approval to allow in more refugees, Zogby said the president could be wary of risking a backlash at a time when he is keen to secure lawmakers' support for a nuclear deal between Iran and world powers, including the United States.

TERRORISM FEARS PROMPT CAUTION

Previous efforts to increase the flow of Syrian refugees have met strong headwinds.

In May, 14 US Senate Democrats wrote a letter urging the Obama administration to allow at least 65,000 Syrian refugees to settle in the United States. The following month, Republican Representative Michael McCaul objected to the administration's plans to allow nearly 2,000 this year.

"While we have a proud history of welcoming refugees, the Syrian conflict is a unique case requiring heightened vigilance and scrutiny," McCaul, whose Homeland Security Committee has held hearings on the issue, wrote in a letter to Obama.

"It represents the single largest convergence of Islamist terrorists in history," including Islamic State, al Qaeda and Hezbollah, he continued, adding that US security officials did not have the information they need for effective vetting.

Republican Representative Peter King of New York echoed that on Monday, saying there was a clear consensus at the hearings that terrorism was a concern.

"We have to have a very, very thorough vetting process," King said on CNN.

The UN High Commissioner for Refugees is responsible for selecting refugees deemed eligible for resettlement and spokeswoman Melissa Fleming said it has submitted more than 16,300 Syrian refugees for resettlement in the United States.

US consular and security officials, including from the Department of Homeland Security, then vet the applicants overseas before allowing them to board a US -bound plane.

Kevin Appleby, director of migration policy at the U.S. Conference of Catholic Bishops, said in an interview that the security worries over Syrians were misplaced, given the intense background checks on refugees.

But more resources would have to be allocated for faster vetting. For example, Appleby said, the United States does not process Syrian refugees from Europe but from Jordan and elsewhere in the Middle East, where most of the refugees are.

DHS and other government officials were not available to discuss the issue on Monday's Labor Day federal holiday.

Pope Francis is likely to call on the United States to live up to its values as a nation that provides safe haven during his U.S. visit this month, Appleby said.

The Conference of Catholic Bishops has long advocated for more Syrians to be allowed in and believes the country could absorb 100,000.

"It is do-able. It's certainly do-able from our end in terms of resettling them in the United States," Appleby said, pointing to the US absorption of Vietnamese refugees during the Vietnam War. "It's just a matter of political will."