Russia's foreign minister says Moscow 'will react' if the EU imposes new sanctions over the crisis in Ukraine.
Europe's already levelled tough measures at Russia but says these will increase if they don't keep to a peace deal agreed on Friday.
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A ceasefire between Ukrainian troops and pro-Russian rebels appears to have held overnight.
Sky's Katie Stallard is in Mariupol in eastern Ukraine, and says it's a tense time for troops on the ground
