The UN said the latest reports from Ukraine show the need for "immediate de-escalation of the conflict."
The UN spokesperson said the organisation was not able to verify reports of Ukrainian shelling of Russian armoured convoy, which Ukraine said crossed border into Ukraine during the night.
Russia has denied that its troops entered its neighbour's territory.
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Armed police have taken part in a dramatic training exercise aimed at recreating the chaos of a Paris-style terror attack.
After a remarkably mild November - a notable mild start to the new month.
The Facebook founder revealed the plan as he and wife Priscilla Chan announced the birth of their baby daughter, Max.