Kazimierz Marcinkiewicz, the acting mayor of Poland's capital Warsaw, cancelled a planned trip to Berlin yesterday, arguing that he could not visit the city while a controversial exhibition was running that in part commemorates the expulsion of Germans from Poland after 1945.

Mr Marcinkiewicz, Poland's prime minister until last month, was due to travel to Berlin yesterday to mark the 15th anniversary of a partnership between the two capitals. The move marks a furtherworsening of relations between Germany and Poland, following a series of recent diplomatic clashes.