United Airlines' US flights grounded due to 'network connectivity issue'

United Airlines flights are grounded across the US due to an unknown technical issue.

The issue has impacted flights nationwide.

It is unclear when it began, but tweets from passengers as early as 5:30am stated they were delayed.

United Airlines has tweeted to say it has experienced a network connectivity issue which it is working to resolve.

We experienced a network connectivity issue. We are working to resolve and apologize for any inconvenience.

— United Airlines (@united) July 8, 2015

3.33pm UPDATE: United Airlines flights are no longer grounded.

The Federal Aviation Administration blamed the ground stop on "automation issues."

We're recovering from a network connectivity issue & restoring flight ops. We’ll have a waiver on http://t.co/ufFoKFTNNe to change flights.

— United Airlines (@united) July 8, 2015