The agencies, under the NSA's surveillance program focused on foreign terrorism suspects, are able to query U.S. communications collected inadvertently. The "backdoor search loophole" allows the agencies to query the U.S. communications in an exception to FISA, which otherwise prohibits the NSA from intentionally targeting U.S. residents.
In June, the House of Representatives voted to close that so-called loophole by requiring the NSA to get a court-ordered warrant to search U.S records in its possession.
While Walsh's letter didn't give a specific number on the FBI searches, it noted that the NSA approved the search of the content of U.S. electronic communications in 198 cases in 2013. The NSA also queried the collected foreign intelligence metadata 9,500 times in 2013 using U.S. resident search terms, the letter said.
The CIA conducted less than 1,900 searches of U.S. communications during 2013, the letter said.
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