Russia’s invasion of Ukraine is entering a new phase, promising a more deadly time ahead for the country’s civilians and its remarkably determined army, according to Western military officials.

Early signs are that Russian commanders are abandoning the approach that marked the first days of the conflict, in which they relied on lightning strikes into cities they assumed would be half-heartedly defended, the officials said.

After multiple failures — highlighted by images Monday morning of a column of Russian heavily armored Tigr vehicles destroyed after trying to punch into Kharkiv, Ukraine’s second largest city — officials from the U.S. and allied nations expect more indiscriminate tactics as Russian forces seek to suppress resistance.