The top United States transportation official has said work being performed on an antiquated telecommunications system could be to blame for a rare, hours-long US Federal Aviation Administration (FAA) ground stop that halted all air traffic inside the country.

At a news conference in Washington, DC, on Saturday, US Transportation Secretary Sean Duffy spoke about routine maintenance that was performed on Friday to upgrade a router from copper to fibre at a “very remote location”.

Duffy said “contractor error or a faulty piece of equipment” caused the router in question to start flooding other ones in the country’s air traffic control system.

“We had 1,000 connection attempts ever four to five seconds,” he told reporters at the Transportation Department.

When those connection issues caused disruption in radar feeds and communications between air traffic controllers and aeroplanes, Duffy said a ground stop was ordered.

“When we see that, your safety is paramount. We shut down the airspace,” he said.

The Transportation Department identified the contractor of Friday’s maintenance as L3Harris, a US-based aerospace and defence company that has been tasked with modernising the communications system for the FAA.

“What we’re working to determine was whether we had incompetence, meaning was it … installator error from L3Harris? Or did they install a faulty router?” Duffy said. “We haven’t determined what the fault was.”

Duffy added that L3Harris, which he said had performed decades of work for the FAA, “didn’t meet the moment”.

“They own this network. They’re our prime contractor. I can’t go somewhere else. They own it,” he said. “Or was it a faulty router? And we’re going to find that out. And frankly, we’re going to hold people accountable.”