German chancellor Angela Merkel has reiterated that she considers Britain's decision to leave the European Union irrevocable.

Britain voted narrowly to leave the EU in a referendum June 23 but Prime Minister Theresa May has yet to formally trigger the process of negotiating the country's exit from the 28-nation bloc.

Mrs Merkel said in an interview released by her party: "The whole process of the exit still lies ahead of us, but the decision is irrevocable."

She added that the decision is a test for the EU, and said: "Now we must negotiate on the basis of our interests. And 'negotiate' means, above all, strengthening common projects."

Mrs Merkel said the EU offers its members a strong voice in the world that individual countries would not have.

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