The U.S. State Department has shut down its entire unclassified email system after a suspected intrusion - and technicians are now working to beef up email security systems, according to the Associated Press.

There is no evidence that classified email systems were accessed, according to The Guardian's report.

A department official said that ‘activity of concern’ was detected in the email security system around the same time as attackers targeted the White House network in late October.

The Washington Post reports that some State Department staff have switched to using Gmail while the worldwide email system was taken down.

Email security: No classified systems affected, officials claim

It’s not clear how the two attacks were linked, ZDNet says.

During the incident involving the unclassified systems at the White House, anonymous White House sources were keen to emphasise that there was no evidence that the White House’s classified network had been hacked.

A State Department official said that a scheduled shutdown of some internet-linked systems was scheduled for late Friday, and the Department shut down its worldwide email system to make security improvements.

Unknown attackers

Both the White House and the State Department have been quiet on who the attackers were - whether state-sponsored or independent - but have said that no classified information was accessed in the attacks.

ZDNet points out that other agencies such as the U.S. Postal Service and National Weather Service have recently reported attacks, but again it’s unclear whether these are related.