The US state department's unclassified email systems were the victim of a cyberattack in recent weeks, around the same time as the White House systems were breached, according to media reports, Reuters reported.
The state department's network was breached last month. However, the department did not disconnect the affected systems until over the weekend, the federal technology information website nextgov.com reported.
It said abnormal activity in the email system had been detected as recently as late October.
The state department breach comes after similar intrusions disclosed in recent months at the White House, the Office of Personnel Management and, only last week, US Postal Service (USPS) and National Oceanic and Atmospheric Administration (NOAA).
According to USPS, it was the victim of an intrusion that might have compromised the personal information of over 800,000 employees, as also data on customers who contacted its call centre during the first eight months of this year. Four of the agency's websites were affected in the NOAA case.
The state department cyberattack was first reported Sunday by The Associated Press.
According to The New York Times, the intrusion did not affect any of the department's classified systems.
Meanwhile, wwindowsitpro.com reported that it was not clear if the state department breach was related to previous events involving the White House, USPS, National Weather Service, and NOAA, among other agencies.
The department quietly shut down its email system on Friday to consolidate defences after detection of an "activity of concern" and announced the breach two days later.
Reuters reported an unnamed state department official as saying the department was implementing improvements to the security of its main unclassified network during a scheduled outage of some internet-linked systems.
He added, this had impacted some of the department's unclassified email traffic and its access to public websites from its main unclassified system. He added the systems were expected to be up and running soon.
According to Reuter's source, the breach was related to an earlier and similar breach of the unclassified portion of the White House email system, which had also led to a temporary shutdown of the service, and did not involve unclassified email.
As regards the source of the attacks, earlier events were suspected to be the handiwork of Russian or Chinese attackers, though it was clear if the governments of those countries were involved. Also the US government had never publicly discussed the origins of the attacks.
According to Dmitry Sergeyevich Peskov, the press attaché for the president of the Russian Federation, his country was not involved.
He said there had been a series of groundless allegations against Russia recently, but these could not be taken seriously any longer unless there was proof.