(CNN) German Chancellor Angela Merkel has challenged Britain's new Prime Minister Boris Johnson to come up with a new plan for Brexit in 30 days.

Merkel told Johnson that he needed to come up with specific proposals on alternatives to the so-called Irish backstop -- the divisive part of the Brexit deal that the UK government wants to abandon -- after he doubled down on a push to remove it without providing any further details.

Speaking at a joint news conference in Berlin on Wednesday evening Merkel said the "UK has to tell us what ideas it has" to solve the backstop issue, adding that "it is not the job of the chancellor" to find a solution.

"We always said we would find a solution in the coming two years," Merkel said. "But possibly, you might find the solution in 30 days, why not? And then we would be a step forward," she added, stressing that every effort should be made to establish a clear plan for the future relationship between Britain and the EU.

Johnson said he welcomed the "blistering timetable" and that the "onus is on us" to find a practical solution to the political deadlock.

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