Germany denounced the parading of European observers held captive by pro-Russian rebels in Ukraine as "revolting", and said Moscow had a duty to press its separatist allies to free the prisoners.
"The public parading of the OSCE observers and Ukrainian security forces as prisoners is revolting and blatantly hurts the dignity of the victims," German Foreign Minister Frank-Walter Steinmeier said in a statement.
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Kurt Cochran and his wife Melissa had been visiting London from the US to celebrate their 25th wedding anniversary and were due to fly home.
The Government has previously described the new coin - which enters circulation tomorrow - as "harder to counterfeit than ever before".
The European bloc said that Russia should release hundreds of people it arrested at anti-government protests and rallies.