Flights grounded across US as homeland security secretary says no indication of an attack

Summary:
Flights have been grounded across the US due to an air traffic control communications issue - here's what we know so far

There's no indication that this is an attack against the US, the homeland security secretary says, adding that "everybody's safe" - what else did he say?

Markwayne Mullin sought to reassure the public, saying repeatedly that this isn't "another 9/11", our Washington correspondent writes...