Image caption Verizon said it had trained tens of thousands of workers to replace those on strike

About 45,000 workers at US telecommunications giant Verizon Communications have gone on strike after failing to reach agreement on new contracts, unions have announced.

Communications Workers for America said Verizon had "refused to move from a long list of concession demands".

They said striking would continue until the firm "starts bargaining seriously".

Verizon said it would continue to do its part to reach a new contract that "reflects today's economic realities".

"It's regrettable for our employees and our customers that the CWA and the International Brotherhood of Electrical Workers have decided to walk away from the table instead of working through the issues," said Marc Reed at Verizon.

"It's our intention that under a new contract, Verizon employees will continue to receive competitive pay and benefits programmes."

The company said it had trained tens of thousands of managers, retired workers and others to fill in for striking staff.

Verizon Wireless customers and services would remain unaffected by the strike, it added.

'Fair agreement'

The CWA said it had taken the "unprecedented" step of striking because Verizon "continued to strip away 50 years of collective bargaining gains for middle-class workers and their families".

It added: "Members are prepared to return to work when management demonstrates the willingness to begin bargaining seriously for a fair agreement."

Negotiations between the unions and Verizon began on 22 June.

Verizon employs a total of almost 200,000 people.