The FBI is probing a possible cyberbreach of numerous company email accounts belonging to New York Times reporters by Russian government-linked hackers, a law enforcement source close to the investigation told Fox News on Tuesday.

The investigation, which is ongoing, is looking into how and how far the perpetrators infiltrated the Times email accounts in question. It was not exactly known how many New York Times email accounts may have been compromised, according to law enforcement sources.

The latest apparent hacking adds to the laundry list of recently disclosed Russia-involved hacks of high profile U.S. organizations.

In recent months, Fox News has reported that Kremlin aligned hacking groups are believed to have been behind the intrusions of the DNC, DCCC, Clinton presidential campaign, and the Clinton Foundation.

A law enforcement source warned of a domino effect playing out in cyberspace where these hackers “island hop” to other targets after compromising an entity. This was previously demonstrated in the Clinton campaign breach, where Russian hackers were able to gain access to a campaign network through the DNC.

It is commonplace for Kremlin-aligned hacking groups to target journalists who portray the Putin regime in an unfavorable light, a law enforcement source told Fox News. Of particular concern, according to this source, is the potential that these reporters’ sources may be revealed and compromised as a result of the New York Times intrusion.

The FBI declined to comment on the targeting of New York Times reporters, but has publicly acknowledged it is investigating the intrusions of the DNC and DCCC.

New York Times spokeswoman Eileen Murphy would not confirm the FBI's investigation, but said, "We have seen no evidence that any of our internal systems, including our systems in the Moscow bureau, have been breached or compromised."

Earlier, Murphy said: "Like most news organizations we are vigilant about guarding against attempts to hack into our systems. There are a variety of approaches we take up to and including working with outside investigators and law enforcement."

CNN first reported the breach of reporter email accounts and added that other U.S. news organizations were also targeted. The source speaking to Fox News was unaware of other reporters at different agencies who may have been targeted.

In 2013, the Syrian Electronic Army claimed responsibility for breaking into the Times' online home page, as well as tweeting a false story from The Associated Press' account about a bomb at the White House.

Last month, a hack of Democratic National Committee emails led several DNC officials to resign. The White House said Russian operatives may have been responsible for sending the leaked emails to Wikileaks.

As Fox News has previously reported, cybersecurity analysts have implicated such Russia-linked cyber militias with carrying out web-based attacks against a number of foreign entities over the past several years. Multiple sources familiar with the research behind these attacks tell Fox News that among Russia’s targets have been the U.S. Departments of State and Defense, White House staffers, NATO, and segments of the Ukrainian government.

Fox News' Matt Dean and The Associated Press contributed to this report.