Rebels press Ukraine offensive, Obama promises steps against Russian-backed 'aggression'

A Ukrainian serviceman stands guard at his position in the village of Luhanska, Luhansk region January 24, 2015. REUTERS/Oleksandr Klymenko

NEW DELHI/KIEV (Reuters) - Pro-Moscow rebels, backed by what NATO says is the open participation of Russian troops, pressed on with their offensive on Sunday after restarting the war in eastern Ukraine with the first all-out assault since a truce five months ago.

U.S. President Barack Obama said Washington was considering all options short of military action to isolate Russia. The European Union called an emergency meeting of foreign ministers of its 28 member states.