WASHINGTON—Ukraine’s weekend attacks against military airfields deep inside Russia signal the long-stalemated war is entering a perilous phase, with both sides seemingly intent on escalation and prospects for a U.

It restated Moscow's demands that Ukraine become a neutral country - ruling out membership of NATO - and that it protect the rights of Russian speakers, make Russian an official language and enact a legal ban on glorification of Nazism. Ukraine rejects the Nazi charge as absurd and denies discriminating against Russian speakers.

Senior Russian security official Dmitry Medvedev also vows ‘retribution’ for Kyiv’s attacks on strategic bomber bases