The first trucks from a humanitarian aid convoy sent into Ukraine have returned to Russia.
Their journey into east Ukraine was not sanctioned by the Ukraine government and drew condemnation from the US and Germany.
German Chancellor Angela Merkel is due to arrive in Ukraine to discuss the situation.
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"Africa is very important for the United States."
The incident happened at around 8pm local time on Thursday evening.
The Foreign Secretary said "good connections" were important, and suggested the Channel Tunnel might simply be "a first step."