As Republican leaders in Congress prepare to block Syrian refugees from the United States, one lawmaker proposed requiring three national security chiefs to certify personally that each refugee admitted from Iraq or Syria is not a threat.

The Republican chairman of the House of Representatives Homeland Security Committee, Michael McCaul, said his bill would strengthen security measures for all refugee populations seeking to enter the United States.

It also would stipulate that no Syrian or Iraqi refugee can enter the United States until Congress receives certification that they are not a national security threat, he said in a statement late on Tuesday.

"The bill requires the nation's top security officials - the Secretary of Homeland Security, the Director of the FBI, and the Director of National Intelligence - to certify before admitting any Syrian or Iraqi refugee into the United States that the individual does not represent a security threat," McCaul said.

House Republican leaders, worried about Islamic State attacks after Friday's killings of 129 people in France, on Tuesday threatened to suspend the administration's plans to admit 10,000 Syrian refugees in the coming year.

McCaul said legislation was necessary because the president was unlikely to halt the program.

Individual certification for these refugees, who already undergo a screening process that can take between 18 and 24 months and involves multiple U.S. security agencies, is likely to slow that process down even further.

Obama administration officials have said Syrians seeking to enter the United States undergo the toughest security screening of any group. Obama, traveling in Asia, on Tuesday called attempts to block entry "offensive and contrary to American values."

House Speaker Paul Ryan said he planned to bring legislation to "pause" the U.S. refugee program for a vote on Thursday.

Democratic Representative Keith Ellison of Minnesota, the first Muslim elected to Congress, said that would send the wrong message to Islamic State, also known as Daesh.

"I think to put our program on pause might signal to Daesh that they're having an effect on what we do," Ellison told CNN. "Do you really want Daesh to dictate terms to the United States?"