Reuters has cited a German government source as saying that the US Administration cancelled Mike Pompeo's visit to Berlin over "international security issues".
A US Embassy spokesperson previously announced the cancellation of the talks citing scheduling conflicts.
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The State Department earlier said that Pompeo "looks forward to being in Berlin soon" to participate in an "important set of meetings" that had been scheduled.
There have been no immediate comments about the meeting's postponement from Merkel or Maas.
It is unclear where the US Secretary of State will head next.
During his visit to Germany, Pompeo was expected to address the issue of the Nord Stream 2 gas pipeline.
The United States has repeatedly voiced objections to the initiative, claiming that the construction of the pipeline was Moscow's means of exercising pressure on the European Union.
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Moscow has denied the allegations, calling Nord Stream 2 a purely commercial project that should not be politicised.
Nord Stream 2 is a joint venture between Russian gas giant Gazprom and five European companies — Germany's Uniper and Wintershall, France's Engie, Austria's OMV and Anglo-Dutch Royal Dutch Shell.
The project, due to be completed before the end of this year, aims to deliver 55 billion cubic metres (1.9 trillion cubic feet) of Russian natural gas annually to the European Union.
