Two civilians have been killed during fighting in Donetsk.
Ukrainian forces have now seized control of the city's airport after vowing to press on with a military offensive "until not a single terrorist" was left.
More than 30 rebels are thought to have died in the clashes.
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The announcement came a day after a famine was declared in two areas of South Sudan following three years of civil war and severe inflation.
It is unclear what their alleged plans were.
Anti-terror police are currently questioning the men who were arrested at three separate locations in France.