A spokesman for the US State Department revealed that the agency's unclassified email systems have been hacked.
State Department spokesman Jeff Rathke told Reuters that they have detected an "activity of concern" some weeks ago.
He also added that they believe that the intrusion was part of a recent similar cyber attack on White House's unclassified computer networks.
Rathke firmly believes that no classified data has been compromised. "We have no reason to believe classified information was compromised."
"The State Department, like any other large organization that has a global span, is a constant target of cyber attacks," he said.
As of press time, parts of the unclassified system have already been shut down. This means that employees of the department are now disallowed to access the Internet through their unclassified system.
They also cannot "reliably receive e-mails from people outside the agency," Reuters added. It is still unknown when it will be back to normal operations.
But a CBS News report said that the systems "will be operating as normal in the near future." It also said that there is a possibility that the people responsible for the breach may not be discussed.
Lawmakers are set to be informed by the State Department about the cyber attack, Reuters reported citing Representative Elijah Cummings. The State Department has been asked by Congress to give more details about the attack on January 5. The report also confirmed that the military's systems have not been affected by the breach.
The similar intrusion on the White House was earlier believed to be perpetrated by some hackers working for the Russian government. A Washington Post report said that no damage has been made in any of the systems. The cyber attack prompted some White House staffers to replace their passwords. They also shut down the Intranet or VPN access, unidentified sources told the Washington Post.
"We've been hearing a series of groundless allegations against Russia recently...So we can't take them seriously any longer unless there's proof," Dmitry Peskov, a spokesman for Russian President Vladimir Putin, told CNN.
A week ago, Latinos Post also reported that the U.S. Postal Service was hacked, compromising over 800,000 employee information including names, birth dates, Social Security numbers, addresses, beginning and end dates of employment and emergency contact information. The intrusion which was discovered in September has already been investigated by the Federal Bureau of Investigation and other postal investigatory agencies.
The National Oceanic and Atmospheric Administration has also been a victim of cyber attacks. It was reported last week that four of NOAA's sites were breached. NOAA spokesman Scott Smullen was cited in a separate Washington Post report confirming the attacks. He however did not provide further details about it saying that an investigation is being done. But it noted that China is believed to be behind this particular intrusion.