The debate over whether to allow Syrian refugees to settle in the US took a dark twist after a leading presidential candidate likened those fleeing the violence in the Middle East to “rabid dogs”.

Republican Ben Carson told a campaign event in Mobile, Alabama, that allowing Syrian migrants into the US could put Americans at risk.

“If there is a rabid dog running around your neighborhood, you’re probably not going to assume something good about that dog,” he said on Thursday, according to Reuters

A group of migrants walks to a refugee reception centre after arriving by raft from Turkey onto the island of Lesbos (Getty)

“By the same token, we have to have in place screening mechanisms that allow us to determine who the mad dogs are, quite frankly.”

The US is riven by debate over whether or not to permit the entry of refugees fleeing Syria, which has suffered from the violence of more than four years of civil war.

President Barack Obama has said he wants to admit 10,000 refugees within a year, after close vetting.

A number of campaigners have called that figure too low and pointed to nations such as Germany that have accepted hundreds of thousands of people.

But in the US, a number of Republicans have suggested Mr Obama is allow too many to enter. The governors of more than 30 states have said they do not want refugees from Syria and will do all they can to block them.

Two Syrian families were forced to travel to Connecticut after the governor of Indiana, where they were initially due to be settled, said they would not be welcome there.

On the same day that Mr Carson spoke, the US House of Representatives passed Republican-backed legislation to suspend Mr Obama’s programme to passed admit the 10,000 refugees in the next year. The president has said he would veto any such legislation.

Concern in the US about the purported danger presented by the refugees - something for which Mr Obama mocked Republicans - has intensified after an unconfirmed report that one of the Paris attackers may have entered Europe among migrants registered in Greece.

Ibrahim Hooper, spokesman for the Washington-based Council on American-Islamic Relations, denounced Mr Carson's comments as “unconscionable”, saying they pointed to a "complete disregard” for American Muslims.

“It really is unconscionable that he would stoop to such levels in smearing people who are fleeing violence and oppression, seeking a better life. Something he, himself, would do if put in the same circumstances,” he said.