Russia-Ukraine war: Key things to know about the conflict

The battle for Ukraine's cities is thundering across its suburbs, with the Ukrainian military retaking a key neighborhood near Kyiv and the invading Russian forces increasing air raids that have caused uncounted deaths and sent millions of people fleeing.

Ukraine's military said early Tuesday it had forced Russian troops out of a strategically important Kyiv suburb, following fierce fighting. However, Russian forces were partially able to take three northwest suburbs where there's been fighting for weeks.

The port city of Mariupol continues to suffer acutely. Civilians making the dangerous escape from the embattled southern port hub described fleeing through street-to-street gun battles and past unburied corpses as steady Russian bombardment tried to pound the city into submission. There was no immediate sign of a diplomatic breakthrough that could bring even temporary relief.

Here are some key things to know about the conflict:

WHY ARE SUBURBS TURNING INTO BATTLEFIELDS?

The suburbs could be a barrier to Ukraine's cities or a doorway for Russian troops, with the capital of Kyiv believed to be Moscow's primary military objective in Vladimir Putin's war.

Outside devastated Mariupol, the Kremlin’s ground offensive has advanced slowly, knocked back by lethal hit-and-run attacks by the Ukrainians.

The regained Kyiv suburb allowed Ukrainian forces to retake control of a key highway to the west and block Russian troops from surrounding the capital from the northwest.

Ukraine’s Defense Ministry said Russian forces advancing toward Kyiv were able to partially take northwest suburbs of Bucha, Hostomel and Irpin, some of which had been under attack almost since Russia’s military invaded on Feb. 24.

Still, Putin’s forces are increasingly concentrating their air power and...