A separatist leader in the eastern Ukrainian city of Slaviansk says he believes detained OSCE observers have a Kiev "spy" in their group, Reuters reported.
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Groups of dairy farmers have milked supermarket shelves dry across the country in a protest against falling prices.
Seasonal rains have battered the country since late June with more than 150,000 people affected by floods and landslides.
The bus reportedly hit a tree near Russell Square.