Luhansk governor says situation 'extremely difficult'. Kremlin says captured Americans are mercenaries. European Union to decide on Ukraine membership bid this week. Russia threatens retaliation against Lithuania.

Ukraine acknowledged on Tuesday difficulties in fighting in its east as Russian forces regrouped after stepping up pressure and making advances on two cities ahead of an EU summit this week expected to welcome Kyiv's bid to join the bloc.

Luhansk governor says situation 'extremely difficult'. Kremlin says captured Americans are mercenaries. European Union to decide on Ukraine membership bid this week. Russia threatens retaliation against Lithuania. 

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