The BBC World Service will be eclipsed by the Voice of America as the world's leading news provider as a result of sweeping cuts to its staff and budget, a senior union official warned today.

World Service staff are being briefed today about cuts that will lead to the loss of up to 650 jobs – more than a quarter of the operation's employees – and the closure of a number of its shortwave services.

Jeremy Dear, the general secretary of the National Union of Journalists, said the loss of the shortwave broadcasts would lead to a sharp drop in the World Service's global reach.

"For the very first time the BBC World Service will no longer be the leading international news provider by audience size. It will be overtaken by the Voice of America," Dear told BBC Radio 4's Today.

"We are certainly surprised by the scale of it. The BBC World Service has had its funding cut by government by around 16% and yet we are looking at around 25% job losses. We think it will do irreparable damage to large parts of the World Service."

Dear said the cuts would have a "significant impact on the World Service's global presence and reputation".

He added: "We are concerned about the jobs but we are also concerned about the services that people provide.

"We have asked MPs to review the nature of the cuts. For example one of the services that is going to be cut is the Albanian service on the grounds that it is no longer needed, just days after 300,000 people took to the streets of Albania and three people are shot dead.

"We think these services are absolutely vital and we need the World Service to be protected ... [foreign secretary] William Hague and the government need to come up with more money to protect these services."

Former BBC Radio 4 controller Mark Damazer today called on the BBC to reverse cuts to the World Service when it takes over its funding in 2014.

"The deficit had to be dealt with. I have no quarrel with the idea that the BBC as a whole could not be spared," wrote Damazer in today's Guardian.

"But I hope that when the BBC takes over the funding of the World Service it will realise that it may need more funding than it is about to get."

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