In a statement today, the 28 European Union leaders said Moscow had to take four steps, among them clear backing for the Ukraine government's peace plan, by Monday June 30.
The leaders "will assess the situation and, should it be required, adopt necessary decisions," the statement said.
The leaders underlined their "commitment to reconvene at any time for further significant restrictive measures," it added.
Among the other conditions listed were that Russia agree a verification mechanism, monitored by the OSCE, on a Kiev ceasefire in eastern Ukraine with pro-Russian rebels and "for the effective control of the border."
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Four observers from the Organisation for Security and Cooperation in Europe abducted on May 26 by pro-Russian rebels were freed Thursday but several others are still being held.
The EU has so far imposed visa bans and asset freezes on more than 60 Russia and Ukraine figures for their role in stoking the crisis but have so far baulked at outright sanctions on important economic sectors despite strong pressure from Washington.
Today's statement noted that member states have been preparing such sanctions "so that further steps can be taken without delay."
Earlier today, Poroshenko signed an association accord which offers Ukraine closer economic and political ties and which was immediately denounced by Moscow.