England fans heading home from the Warsaw washout said they weren't surprised the match was called off, but they said organisers were wrong not to close the roof because at top-level sport "games should not be called off".
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Political parties across the country suspended their General Election campaigns following the Manchester Arena terror attack on Monday.
Investigators believe Mr Kushner has significant information relevant to their inquiry, officials told NBC News.
The men were detained as part of an investigation by MI5 and the Metropolitan Police's Counter Terrorism Command.