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US president says threat of Russian invasion very high', after Ukraine government source says shelling looks like provocation'

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Some more detail has emerged regarding the denial from Ukrainian government forces over accusations of having targeted separatist positions in the country's east. Ukraine says its troops were fired upon but did not retaliate.

A duty press officer of the Ukrainian Joint Forces Operation told Reuters by telephone:

Despite the fact that our positions were fired on with prohibited weapons, including 122mm artillery, Ukrainian troops did not open fire in response.