Washington (CNN) US authorities have prepared charges to seek the arrest of WikiLeaks founder Julian Assange, US officials familiar with the matter tell CNN.

The Justice Department investigation of Assange and WikiLeaks dates to at least 2010, when the site first gained wide attention for posting thousands of files stolen by the former US Army intelligence analyst now known as Chelsea Manning

Prosecutors have struggled with whether the First Amendment precluded the prosecution of Assange, but now believe they have found a way to move forward.

During President Barack Obama's administration, Attorney General Eric Holder and officials at the Justice Department determined it would be difficult to bring charges against Assange because WikiLeaks wasn't alone in publishing documents stolen by Manning. Several newspapers, including The New York Times, did as well. The investigation continued, but any possible charges were put on hold, according to US officials involved in the process then.

Going after Assange

The US view of WikiLeaks and Assange began to change after investigators found what they believe was proof that WikiLeaks played an active role in helping Edward Snowden, a former NSA analyst, disclose a massive cache of classified documents.

Assange remains holed up in the Ecuadorian embassy in London , seeking to avoid an arrest warrant on rape allegations in Sweden . In recent months, US officials had focused on the possibility that a new government in Ecuador would expel Assange and he could be arrested. But the left-leaning presidential candidate who won the recent election in the South American nation has promised to continue to harbor Assange.

Last week in a speech at the Center for Strategic and International Studies in Washington, CIA Director Mike Pompeo went further than any US government official in describing a role by WikiLeaks that went beyond First Amendment activity

He said WikiLeaks "directed Chelsea Manning to intercept specific secret information, and it overwhelmingly focuses on the United States."

"It's time to call out WikiLeaks for what it really is: A non-state hostile intelligence service often abetted by state actors like Russia," Pompeo said.

US intelligence agencies have also determined that Russian intelligence used WikiLeaks to publish emails aimed at undermining the campaign of Hillary Clinton, as part of a broader operation to meddle in the US 2016 presidential election. Hackers working for Russian intelligence agencies stole thousands of emails from the Democratic National Committee and officials in the Clinton campaign and used intermediaries to pass along the documents to WikiLeaks, according to a public assessment by US intelligence agencies.

Still, the move could be viewed as political, since Assange is untouchable as long as he remains in the Ecuadorian embassy, and Ecuador has not changed its stance on Assange's extradition.

Stepping up efforts

Attorney General Jeff Sessions said at a news conference Thursday that Assange's arrest is a "priority."

"We are going to step up our effort and already are stepping up our efforts on all leaks," he said. "This is a matter that's gone beyond anything I'm aware of. We have professionals that have been in the security business of the United States for many years that are shocked by the number of leaks and some of them are quite serious. So yes, it is a priority. We've already begun to step up our efforts and whenever a case can be made, we will seek to put some people in jail."

"We've had no communication with the Department of Justice and they have not indicated to me that they have brought any charges against Mr. Assange," said Assange's lawyer, Barry Pollack. "They've been unwilling to have any discussion at all, despite our repeated requests, that they let us know what Mr. Assange's status is in any pending investigations. There's no reason why WikiLeaks should be treated differently from any other publisher."

Pollack said WikiLeaks is just like the Washington Post and the New York Times, which routinely publish stories based on classified information. WikiLeaks, he says, publishes information that is in "the public's interest to know not just about the United States but other governments around the world."

Freedom of speech?

Assange has also compared WikiLeaks to a news media organization that uses documents provided by whistleblowers to expose the actions of governments and powerful corporations.

"Quite simply, our motive is identical to that claimed by the New York Times and The Post -- to publish newsworthy content," Assange wrote in a recent op-ed in The Washington Post . "Consistent with the U.S. Constitution, we publish material that we can confirm to be true irrespective of whether sources came by that truth legally or have the right to release it to the media. And we strive to mitigate legitimate concerns, for example by using redaction to protect the identities of at-risk intelligence agents."

In his speech last week, Pompeo rejected that characterization and said Assange should not be afforded constitutional free speech protections.

"Julian Assange has no First Amendment freedoms. He's sitting in an Embassy in London. He's not a US citizen," Pompeo said.

Rep. Peter King, R-New York, told CNN's Wolf Blitzer that based on CNN's reporting, "I'm glad that the Justice Department has found a way to go after Assange. He's gotten a free ride for too long."

King said Assange has "caused tremendous damage to our national security, put American lives at risk."

But Ben Wizner, director of the American Civil Liberties Union's Speech, Privacy and Technology Project, argued that US prosecution of Assange sets a dangerous precedent.

"Never in the history of this country has a publisher been prosecuted for presenting truthful information to the public," Wizner told CNN. "Any prosecution of WikiLeaks for publishing government secrets would set a dangerous precedent that the Trump administration would surely use to target other news organizations."

CORRECTION: This story has been updated to correctly describe the allegations against Assange in Sweden and clarify Pompeo's comment about free speech protections.