London's mayor has called on foreign diplomats based in the city to pay the congestion charge.

Ken Livingstone's comments followed revelations that US and German staff have refused to pay.

Under the 1961 Vienna convention diplomats are exempted from paying local taxes.

But a spokesman for the mayor said: "The congestion charge is not a tax. It is a charge for a service.

"All staff at the American embassy should pay the congestion charge, in the same way as British officials pay road tolls in the United States.

"To refuse to do so in either case is to break the law of the host country."

And the leader of the assembly Liberal Democrats, Graham Tope, backed the mayor's position.

He said the embassy's assertion that it did not have to pay under the Vienna convention was "an insult to Londoners".

"This is not Baghdad, this is London and they should respect the rules of the country they are guests in," Tope added.

"If it was a breach of the Vienna convention then why hasn't every other country's embassy in London also refused to pay the congestion charge?

"The Americans are quite happy to cite the Vienna convention, but are all to willing to play fast and loose when it comes to the Geneva convention.

"The mayor is right to stand firm against the Americans' ludicrous refusal to pay the charge."