The US State Department is experiencing a worldwide outage of its unclassified email system, officials said.

"The State Department is experiencing a system-wide unclassified email outage," the Department said in a statement to The Independent. "We are working to restore service as soon as possible. Other communication systems are available and being used."

In a press conference on Friday, State Department spokesperson Heather Nauert described the outage as a "technical glitch". To her knowledge, she said, the outage was not caused by external actors.

Officials said the outage started Friday morning – the same morning President Donald Trump announced he would elevate the Pentagon's US Cyber Command to the level of level of Unified Combatant Command. The move puts the organisation on the same level as units overseeing military operations in the Middle East, Europe and the Pacific.

Mr Trump said the move "will strengthen our cyberspace operations and create more opportunities to improve our Nation’s defence".

"The elevation of United States Cyber Command demonstrates our increased resolve against cyberspace threats and will help reassure our allies and partners and deter our adversaries," he said.