A car bomb has exploded in central Damascus, causing casualties, state television has reported.
A resident in Damascus, who described the explosion as the biggest she had heard in the Syrian capital, said large plumes of smoke were rising from the area.
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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.