By Lindsay Dunsmuir
WASHINGTON (Reuters) - Barring law enforcement authorities' access to encrypted communications would make it easier for Islamic State sympathizers to attack the United States, FBI Chief James Comey told Senate lawmakers on Wednesday.
The Federal Bureau of Investigation is pushing technology companies to let law enforcement authorities have access to encrypted communications to investigate illegal activities. Those companies have resisted, arguing that such access would weaken systems against criminals and computer hackers.
Comey has previously criticized Apple Inc and Google Inc for ramping up encryption.
Comey told a U.S. Senate Judiciary Committee hearing that Islamic State, also known by the acronym ISIL, is imploring supporters through Twitter to carry out attacks. Related conversations often take place via end-to-end encryption mobile communications that are unreadable to anyone other than those sending or receiving the messages.
"The tools we are asked to use are increasingly ineffective," Comey said. "ISIL says go kill, go kill...we are stopping these things so far...but it is incredibly difficult. I cannot see me stopping these indefinitely."
Comey later told the Senate Select Committee on Intelligence that the FBI now estimated more than 200 Americans have traveled or attempted to travel to Syria to fight for Islamic militants.
Comey, citing a lack of reliable data, acknowledged to lawmakers that he did not know how often the FBI cannot access encrypted communications.
Earlier, Comey and Deputy Attorney General Sally Yates rejected the notion that the government is seeking backdoor access to encrypted communications.
"We are not seeking a front door, back door, or any kind of door...but we are seeking to work with the industry," Yates said. She urged Congress to work with Silicon Valley and said they were looking to tailor solutions to individual companies.
Yates said that some technology companies already access users' encrypted information to sell advertisements. She did not rule out introducing legislation on the issue if an agreement with technology companies cannot be reached.
An industry association which represents major software and hardware companies reiterated its stance against government access.
"Weak encryption is essentially no encryption, leaving all consumers vulnerable to breaches of privacy and cybercrime," the group said in a statement.
On Tuesday, a prominent group of computer scientists released a report rebutting U.S. and British government proposals for exceptional access, citing the potential for hacking and abuse.
(Reporting by Lindsay Dunsmuir; Editing by Christian Plumb and Grant McCool)