David Cameron is "gravely concerned" at reports of Russian military vehicles crossing into Ukraine, his spokesperson said.
After speaking to Ukraine's President Petro Poroshenko, the Prime Minister said Russia must not use its humanitarian aid convoy as a pretext for provocation and asked Russia to "demonstrate willingness to find a peaceful solution to conflict in Ukraine."
More top news
The Foreign Office have changed their advice for UK travellers following political unrest in the west African country.
A British built satellite is set to revolutionise weather forecasts by making them more accurate and useful.
Milder Atlantic air drawn into the north with colder, Continental air seeping into the south