Amid mounting pressure on the United States to do more to avert a humanitarian crisis involving Muslim refugees from war-torn Syria, Republican presidential candidate Marco Rubio on Tuesday suggested he would consider a more active U.S. role.

Rubio, a U.S. senator from Florida, told Boston Herald Radio he would want to ensure that arriving migrants were free of ties to international terrorism — a chief concern voiced by critics.

“We’ve always been a country that has been willing to accept people who have been displaced, and I would be open to that if it can be done in a way that allows us to ensure that among them are not … people who are part of a terrorist organization,” he said on the radio program. “The vast and overwhelming majority of people who are seeking refuge are not terrorists, of course, but you always are concerned about that.”

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The Rubio campaign did not immediately respond to an inquiry from LifeZette seeking more details on his thoughts.

Rubio’s comments could feed into lingering distrust among conservative voters over the broader issue of immigration. Rubio was part of the Gang of Eight in the Senate who tried in 2013 to craft a comprehensive immigration reform bill that would provide a path to citizenship for many people who entered the United States illegally.

Rubio has backed off that plan somewhat, saying the effort should have been preceded by a rock-solid commitment to securing the southern border with Mexico.

But he remains an immigration moderate, compared to candidates such as billionaire real estate developer Donald Trump. Last month, Rubio called Trump’s immigration proposal “unworkable.” He also has said he believes the 14th Amendment guarantees citizenship for babies born on U.S. soil — regardless of their parents’ immigration status — and added that he opposes repealing it.

U.S. financial assistance is the most of any country, but international humanitarian groups have called on the United States to do more to provide refuge for the millions of fleeing Syrians.

The United States has contributed more than $4 billion in humanitarian assistance to refugees from Syria, which has been gripped by civil war and is trying to prevent ISIS from taking over its land.

That financial assistance is the most of any country, but international humanitarian groups have called on the United States to do more to provide refuge for the millions of Syrians fleeing the turmoil. Since the start of the Syrian war in 2011, the U.S. has taken in just 1,500 Syrian refugees, and the State Department expects 300 more by October, according to Reuters.

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By contrast, Germany is preparing for 800,000 asylum seekers this year, but Angela Merkel, Germany’s chancellor, called for “mandatory quotas to be set for each country to take a share of (the) displaced people,” CNN reported. The crisis should be solved in the spirit of European solidarity, she said at a Berlin press conference with Swedish Prime Minister Stefan Lofven.

British Prime Minister David Cameron has promised to accept up to 20,000 refugees from camps in Syria over the next five years. French President Francois Hollande said his country would accommodate 24,000 refugees over the next two years.

President Barack Obama has the authority to accept more refugees without congressional approval. Congressional backing, however, would strengthen his hand on the politically sensitive issue.

Already, some congressional Republicans have raised concerns over unwittingly letting terrorists into the United States. Rep. Peter King, R-N.Y., said Monday on CNN, “We have to have a very, very thorough vetting process.”