FBI chief James Comey renewed a call Thursday for broader authority to tap into emerging technologies, saying the Edward Snowden revelations have led to unwarranted mistrust of law enforcement.

Comey said revelations about widespread surveillance have led to a climate which could hinder the ability to catch criminals and terrorists, underscored by new efforts to encrypt smartphones to make them inaccessible to investigators, even with a warrant.

"Perhaps it's time to suggest that the post-Snowden pendulum has swung too far in one direction -- in a direction of fear and mistrust," Comey said in a speech at the Brookings Institution.

"There will come a day -- and it comes every day in this business -- where it will matter a great deal to innocent people that we in law enforcement can't access certain types of data or information, even with legal authorization. We have to have these discussions now."

Comey's comments sought to renew the debate about the FBI "going dark," or being unable to access encrypted calls and messages from new apps and services which fall outside the traditional realm of "wiretaps."

The FBI had been calling for changes to the US law covering wiretapping in 2013, but that debate was shelved after the revelations from former NSA contractor Snowden in June last year about vast surveillance of telephone and online communications.

Comey said the leaked Snowden documents exaggerated the capabilities of agencies like the Federal Bureau of Investigation.

"In the wake of the Snowden disclosures, the prevailing view is that the government is sweeping up all of our communications. Of course, that's not true," he said.

"And if the challenges of real-time interception threaten to leave us in the dark, encryption threatens to lead all of us to a very dark place."

- 'Front door' access -

Comey said the announcements in recent weeks by Apple and Google that they would encrypt their smartphones so that law enforcement cannot access them, even with a warrant, provided a "catalyst" for him to revive the debate from 2013.

The encryption initiatives "energized me to say we have to have a conversation about this," he said.

Comey last month warned that the new encryption by default could lead to problems for law enforcement, even as privacy activists applauded the efforts by the companies.

In his Brookings comments, Comey said he was not looking for a "back door" into devices and systems that could be exploited by malicious actors.

"We want to use the front door, with clarity and transparency, and with clear guidance provided by law," he said.

"We are completely comfortable with court orders and legal process -- front doors that provide the evidence and information we need to investigate crime and prevent terrorist attacks."

Comey said he wants Congress to update the law covering FBI wiretap authority, but also hopes companies will cooperate in this effort "so that criminals around the world cannot seek safe haven for lawless conduct."

"An adversarial posture won't take any of us very far down the road," he added.

- Swift criticism -

Comey's remarks drew swift criticism from civil liberties activists.

Laura Murphy of the American Civil Liberties Union said Comey "is wrong" about encryption.

"Whether the FBI calls it a front door or a back door, any effort by the FBI to weaken encryption leaves our highly personal information and our business information vulnerable to hacking by foreign governments and criminals," she said in a statement.

"We applaud tech leaders like Apple and Google that are unwilling to weaken security for everyone to allow the government yet another tool in its already vast surveillance arsenal."

Nuala O'Connor, president of the Center for Democracy and Technology, also opposed efforts to give special access to law enforcement.

"We debated and settled the question of whether law enforcement should have back doors into communications networks more than 20 years ago," she said.

"Now, more than ever, we need strong security to combat malicious hackers and deter overly intrusive government surveillance. Companies are providing more encryption because it is exactly the type of protection the public wants and needs."