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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The prince laid a floral wreath at one of a group of metal crosses near Wellington Arch in central London.
The group, which also owns Premier Inn, said on Wednesday that it will pursue a ‘demerger of Costa’.
The showers will become more frequent as the day goes on, giving some heavy downpours in places during the afternoon.