The FBI is investigating a series of cyber-attacks on social media accounts of U.S. news outlets carried out by hackers claiming allegiance to the Islamic State group, according to federal authorities and multiple news outlets.

The Albuquerque Journal and Maryland-based TV station WBOC 16's Twitter accounts were some of the first to be hacked on Tuesday morning by Cyber Caliphate, a group that claims to be part of ISIS and is planning a series of cyber-attacks on homes and offices across the U.S., the Associated Press reported.

"You'll see no mercy infidels. We are already here, we are in your PCs, in each house, in each office. With Allah's permission we began with New-Mexico and will come to every state, inshallah," Cyber Caliphate wrote on their Facebook page, which was taken down shortly after. "We won't stop... We know all your personal data: where you live, what you eat, your diseases, and even your health insurance cards."

On Tuesday, the hackers took over the website and Twitter feed of WBOC-TV in Salisbury, Md., before the station wrestled back control of the website, which briefly displayed the extremist group's black-and-white flag and a message saying, "I love you, ISIS."

However the station's Twitter feed remained under the hackers' control on Wednesday, with the group now claiming to have hacked into FBI databases.

Simultaneously, the Twitter feed of The Albuquerque Journal in New Mexico was also targeted, with the newspaper's profile picture being replaced with an image that expressed support for Islamic militants. The hacker group also posted several confidential documents, including photos of driver's licenses belonging to New Mexico residents, inmate profiles and warnings to residents that their confidential information was at risk.

The newspaper had regained control over the feed by mid-day Tuesday. "ABQjournal's Twitter feed and Facebook page were compromised early today," said the newspaper in a statement. "The Journal reached out to Facebook and Twitter to help resolve this issue. Law enforcement agencies have been contacted are investigating."

Craig Jahelka, station general manager at WBOC, told New York Daily News that they have no idea why the group decided to target them.

"We are as baffled as the folks at the Albuquerque Journal are," Jahelka said. "We do not have control over our twitter handle yet, but we have regained control over our website."

Currently, it remains unclear whether the hackers are genuine members or even supporters of the terrorist organization. Tech-savvy pranksters are known to routinely make bogus claims or falsify their allegiances in bids to get attention.

Meanwhile, the FBI was looking into the New Mexico case, FBI spokesman Frank Fisher said, but failed to immediately return a request for comment about whether the Maryland cyber-attack was under investigation, though the station said in its news report on Tuesday that it was speaking to the agency.

"Similar attacks have been quietly happening to media companies across the United States," the FBI was cited as saying in the WBOC report.