MANHATTAN, NY -- The FBI said the number of encrypted devices that the FBI has been unable to access last year has risen.

FBI director Christopher Wray said in a conference Tuesday at Fordham University in New York that the agency couldn't access 7,775 devices in 2017 because the contents were scrambled.

That's up from over 6,900 in October.

Wray said that each device was tied to a specific subject or threat, but did not say how many investigations were affected by the lack of access.

ZDNet filed a Freedom of Information Act request in October to seek answers on the number of investigations impacted, but has not yet received a response beyond an initial acknowledgement.

This is not the first time Wray as FBI director, like his predecessors, has argued that encryption gets in the way of investigations. The so-called "going dark" issue, referring to the inability to gain access to criminals' devices and data, remains a key challenge for the FBI.

"We're not interested in the millions of devices of everyday citizens," he said. "We're interested in the devices that are used to plan or execute terrorist or criminal activity."

Wray called for "thoughtfully designed" solutions to access the contents of phones and devices, calling it a "major public safety issue."

He added that the 7,775 figure is "more than half of all the devices we attempted to access" last year, suggesting the total number could be as high as 15,000 devices. That figure also doesn't take into account other federal agencies, he said.

But he conceded that a solution to the "going dark" issue is "not so clear cut."

Critics have long called any solution a "backdoor," because allowing access for law enforcement would mean hackers could gain unauthorized access too.

Wray said although the FBI "supports strong encryption," it's necessary for the FBI to access the contents of communications as it can be used for evidence. Phone and email metadata records, including the time and date of communications, can be used to draw associations between suspects but it "won't get you very far" in prosecuting a case.

The battle over access to encrypted devices came to a head in 2016 when the Justice Dept. sought to compel Apple to build a backdoor to bypass the encryption on the iPhone that belonged to Syed Farook, who with his wife Tashfeen Malik shot and killed 14 people in San Bernardino, California in December 2015.

Wray said that lawmakers needed to "address gaps" in the laws, without providing specific examples, saying that many were analogous to "traffic laws around the time of the cart and buggy."