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Story highlights

The 500 denials represent almost 7% of all applicants

The US allowed more than 15,000 Syrian refugees in 2016, many of whom are under the age of 14

(CNN) —  

The US government has denied more than 500 Syrian refugee applications since 2011 because applicants had known or suspected terrorism ties, according to House Homeland Security Committee Chairman Michael McCaul.

McCaul cited the numbers he learned from a briefing by law enforcement and intelligence agencies in a letter this week to the acting director of National Intelligence, Michael Dempsey. CNN has obtained the letter.

The 500 denials represent almost 7% of all applicants. McCaul also said he was told in a briefing that “several hundred additional Syrian cases are on hold pending final review for denial on national security grounds.”

The number of terror-related denials, McCaul said, raised new concerns because federal agencies that oversee refugee resettlements are reinvestigating the backgrounds of a number of refugees allowed into the US from Syria.

A technical glitch allowed a small number of refugees to be resettled without a complete check of data on intelligence databases, according to a US official briefed on the matter. It’s not clear how long the glitch affected vetting of refugees and how many are being reinvestigated.

The Los Angeles Times first reported on the glitch.

Law enforcement and intelligence officials said none of the refugees that have so far been reinvestigated have been found to be inadmissible.

The glitch may also have affected the background checks for a broader population of people who were allowed into the United States, according to the US official briefed on the matter.

The US allowed more than 15,000 Syrian refugees in 2016, a large proportion of which are under age 14.

An intelligence official said “refugees are subject to the highest level of security checks of any category of traveler to the United States. No immigration program is completely without risk. We continuously examine options for further enhancements for screening refugees, the details of which are classified.”

A spokesperson for the US Citizenship and Immigration Service said: “The interagency processes for screening all refugee applicants, including Syrians, has been enhanced and improved over time. USCIS continues to work with the law enforcement and intelligence communities to look for ongoing opportunities for improvements for screening all categories of applicants, including the security checks for refugee applicants.”

The USCIS spokesperson added: “Certain details of the security screening processes are held confidential and classified. In addition, it would not be appropriate for USCIS to comment on the internal processes of other federal interagency partners.”

McCaul in his letter asked the DNI and other officials for more information about the glitch.