The FBI and CIA can also query the content of U.S. residents’ electronic communications that the National Security Agency inadvertently collects when targeting foreign terrorism suspects, an intelligence official said.

While privacy advocates have objected to a so-called “backdoor search loophole” allowing the NSA access to electronic communications by U.S. residents, it was unclear until now whether other agencies also had access to those emails, phone calls and other communications.

The information came out in a letter sent by the U.S. Office of the Director of National Intelligence to Senator Ron Wyden, an Oregon Democrat.

While the CIA and NSA conducted thousands of searches targeting U.S. communications in 2013, the FBI does not track number of searches it does, according to the ODNI’s letter. But in any case both the CIA and FBI have access to communications accessed by the NSA, the letter said

The CIA and FBI are allowed to search that information for “foreign intelligence information,” and the FBI also to search it to “find and extract evidence of a crime,” Deirdre Walsh, ODNI’s director of legislative affairs, wrote in the letter.

The letter was sent in response to a question Wyden had asked, during a June 5 hearing, about the number of U.S. searches the NSA was conducting through the Foreign Intelligence Surveillance Act (FISA), a law designed to allow surveillance of foreign suspects.

“The queries in question are lawful, limited in scope, and subject to oversight as approved by the Foreign Intelligence Surveillance Court,” Walsh wrote in response. “Contrary to some claims, there is no loophole in the law, nor is the Intelligence Community conducting unlawful or ‘backdoor searches’ of communications of U.S. persons.”

Wyden: Who's in charge?

Wyden, a long-time critic of NSA surveillance programs, said searches by the CIA and FBI raise serious questions.

“When the FBI says it conducts a substantial number of searches and it has no idea of what the number is, it shows how flawed this system is and the consequences of inadequate oversight,” Wyden said in a statement Monday. “This huge gap in oversight is a problem now, and will only grow as global communications systems become more interconnected.”

Walsh’s letter, sent to Wyden last week and posted by Wyden’s office Monday, said the FBI “does not track how many queries it conducts using U.S. person identifiers.”

That’s troubling, Wyden said. “The findings transmitted to me raise questions about whether the FBI is exercising any internal controls over the use of backdoor searches including who and how many government employees can access the personal data of individual Americans,” he said.

The U.S. Foreign Intelligence Surveillance Court has said the NSA acquires more than 250 million Internet communications every year under the FISA authority, Wyden added. “Even if U.S. communications make up a small fraction of that total, the number of U.S. communications being collected is potentially quite large,” he said

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.