Russian forces attacked several new cities in the latest fighting, targetting two cities in the country's West and one in the East which had previously been a safe haven.
Russian bombardments struck airfields in Lutsk and in Ivano-Frankivsk. Russia has not previously targetted Ukraine's west, and these attacks are the closest so far to the country's borders with NATO countries.
Residential buildings were also hit in Dnipro, a city in the east which had previously been regarded as a safe refuge for civilians.
Elsewhere satellite imagery near the capital Kyiv suggested a change of tactics from Russian forces, with tanks seen to disperse and encircle the city. Correspondents suggest this could be a signal that an all out attack is imminent.
Latest reports show Ukrainian soldiers checking the identification documents of drivers, on the lookout for Russian saboteurs.
In Kyiv and in the beseiged southern part of the country, supplies are fast running out for those Ukrainians who remain to fight. One correspondent described conditions in the battleground city of Mariupol as "primieval".
But the governor of another southern city, Mykolaiv, says defenders have driven Russian forces out.
Across Ukraine, latest estimates suggest more than four million people have fled from their homes.
Latest reports say Russia is about to bolster its own forces with volunteers from the Middle East. Moscow released video footage of a group of fighters, saying they were among 16 thousand Syrians who wanted to join the battle.
Ukraine says it could also come under attack from a new quarter to the north. It claims Russia is set to launch a "false flag" operation, to provide an excuse for Belorussian forces to attack Ukraine.
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